UC-NRLF 


B    3    1ED    3SE 


AMERICAN  SCIENCE  SERIES,  BRIEFER  COURSE 


THE  HUMAN  BODY 


AN 


ELEMENTARY  TEXT-BOOK  OF  ANATOMY, 
PHYSIOLOGY  AND  HYGIENE 


INCLUDING  A  SPECIAL  ACCOUNT  OF  THE  ACTION  UPON  THE 

BODY  OF  ALCOHOL  AND  OTHER  STIMULANTS 

AND  NARCOTICS 


BY 

H.  NEWELL   MARTIN/ D.Sc.,  M.D.,  M.A.,  F.R.S. 

Professor  of  Biology  in  the  Johns  Hopkins  University 

THIRD  EDITION,  REVISED 


NEW  YORK 
HENRY    HOLT    AND    COMPANY 

1889 


> 


BIOLOGY 

LIBRARY 

G 


COPYRIGHT,  1883, 1884, 

BY 

HENRY  HOLT  &  CO. 


PREFACE. 


THIS  elementary  textbook  of  Physiology  has  been  pre- 
pared in  response  to  many  requests  for  a  textbook 
framed  on  the  same  plan  as  the  "Human  Body,"  but 
abridged  for  the  use  of  students  younger,  or  having  less 
time  to  give  to  the  subject,  than  those  for  whom  that  book 
was  designed.  This  demand^  and  the  fact  that  a  second 
edition  of  the  ft  Human  Body  "  was  called  for  within  twelve 
months  of  its  publication,  have  shown  me  that  I  was  not 
wrong  in  believing  that  the  teachers  of  Elementary  Physi- 
ology in  the  United  States  were  ready  and  anxious  for  a 
textbook  in  which  the  subject  was  treated  from  a  scientific 
standpoint,  and  not  presented  merely  as  a  set  of  facts, 
useful  to  know,  which  pupils  were  to  learn  by  heart  like  the 
multiplication  table. 

That  some  instruction  in  at  least  one  branch  of  Natural 
Science  should  form  a  part  of  the  regular  educational  cur- 
riculum is  now  so  generally  admitted  that  there  is  no  need 
to  insist  upon  it.  But  if  this  instruction  simply  means 
teaching  by  rote  certain  facts,  no  matter  how  important 
these  facts  may  be,  the  proper  function  of  Natural  Science 
in  a  system  of  education  is  missed.  Mere  training  of  the 
memory  (no  unimportant-  matter)  is  otherwise  sufficiently 


IV  PREFACE. 

provided  for  in  the  usual  school  and  college  course  of  study : 
the  true  use  of  Natural  Science  in  general  education  is 
different.  It  should  prepare  the  student  in  another  way 
for  the  work  of  subsequent  daily  life,  by  training  the  ob- 
serving and  reasoning  faculties. 

As  a  department  of  science,  modern  Physiology  is  con- 
trolled mainly  by  two  leading  generalisations — the  doctrine 
of  the  "  Conservation  of  Energy"  and  that  of  the  "  Physio- 
logical division  of  labor. "  I  have  endeavored  in  this,  as  in 
the  larger  book,  to  keep  prominent  these  leading  principles  ; 
and,  so  far  as  is  possible  in  an  elementary  book,  to  exhibit 
the  ascertained  facts  of  Physiology  as  illustrations  of  or  de- 
ductions from  them. 

The  anatomical  and  physiological  facts  which  can  be 
described  in  books  of  the  size  of  the  present,  must  be  pretty 
much  the  same  in  all.  Apart  from  the  attempt  above  men- 
tioned to  make  elementary  Physiology  a  more  useful  edu- 
cational instrument  than  it  has  frequently  hitherto  been, 
the  present  volume  differs  from  most  others  of  its  grade  in 
having,  as  foot-notes  or  as  appendices  to  the  chapters,  simple 
practical  directions,  assisting  a  teacher  to  demonstrate  to 
his  class  certain  fundamental  things.  The  demonstrations 
and  experiments  described  necessitate  the  infliction  of  pain 
on  no  animal,  and  require  the  death  of  no  creature  higher 
than  a  frog,  except  such  superfluous  kittens,  puppies  and 
.rats  as  would  be  killed  in  any  case,  and  usually  by  methods 
much  less  merciful  than  those  prescribed  in  the  following 
pages.  The  practical  directions  are,  for  the  most  part, 
reprints  from  a  series  of  such  which  I  drew  up  some  years 
ago  for  a  class  composed  of  Baltimore  teachers ;  those  ex- 
periments which  required  costly  apparatus  have,  of  course, 
been  omitted.  The  interest  which  my  "  Teachers'  Class" 
took  in  its  work,  and  the  good  use  its  members  subsequently 
made  of  it,  have  encouraged  me  to  believe  that  others 
might  be  glad  of  a  few  hints  as  to  things  suitable  to  show 
to  young  students  of  Physiology. 


PREFACE.  V 

It  may  be  well  to  anticipate  a  possible  objection.  A  few 
persons,  some  of  them  worthy  of  respect,  assert  that  no  ex- 
periments on  an  animal  can  be  shown  to  a  class  without 
hardening  the  hearts  of  operator  and  spectators;  even  when, 
in  accordance  with  the  directions  given  in  the  following 
pages,  the  animal  is  anaesthetised  and  while  in  that  condi- 
tion is  killed  or  its  brain  destroyed.  This  from  an  experi- 
ence of  more  than  fifteen  years  in  the  teaching  of  practical 
physiology,  I  know  to  be  not  so.  So  far  as  the  experiments 
described  in  the  present  book  are  concerned,  their  effect  is 
most  certainly  humanizing.  Young  people  are  apt  to  be, 
nofc  callous,  but  thoughtless  as  to  the  infliction  of  pain. 
When  they  see  their  teacher  take  trouble  to  kill  even  a  frog 
painlessly,  they  have  brought  to  their  attention  in  a  way 
sure  to  impress  them,  the  fact  that  the  susceptibility  of  the 
lower  animals  to  pain  is  a  reality,  and  its  infliction  some- 
thing to  be  avoided  whenever  possible. 

As  the  question  of  size  is  no  unimportant  one  in 
relation  to  textbooks  designed  for  junior  students  with 
many  other  subjects  to  learn,  I  may  be  permitted  to  say  that 
though  this  volume  contains  more  pages  than  most  of  those 
with  which  it  will  have  to  compete,  I  believe  it  is  not  really 
larger.  The  extra  pages  are  due,  in  part  to  the  above- 
mentioned  appendices  to  the  chapters,  and  in  part  to  the 
great  number  and  large  size  of  the  figures.  My  publishers 
had  on  hand  electrotypes  of  the  figures  of  the  octavo  edi- 
tion, and  have  been  able  to  utilize  them  in  illustrating  this 
briefer  one  much  better  than  most  textbooks  of  its  scope, 
without  proportionately  increasing  its  price. 

If  I  had  relied  solely  on  my  own  judgment  the  ques- 
tions at  the  foot  of  each  page  would  have  been  omitted.  But 
it  was  strongly  represented  to  me  by  those  whose  opinion 
I  had  reason  to  value,  that  such  questions  were  useful 
in  enabling  a  student  to  test  whether  he  had  mastered  his 
lesson,  and  that  teachers  who 'disliked  such  prearranged 
questions  could  and  would  ignore  them.  I  hope  that 


VI  PREFACE. 

the  pupils  will  use  the  questions  and  that  their  teachers  will 
not. 

Before  concluding,  I  must  express  my  sincere  thanks  to 
Miss  Frances  T.  Bauman,  who  has  given  me  the  benefit  of 
her  many  years'  experience  as  an  eminently  successful 
teacher.  She  kindly  read  a  large  portion  of  the  manuscript, 
and  gave  me  much  advice  of  which  I  have  been  glad  to 
avail  myself.  I  have  also  to  acknowledge  my  indebtedness 
to  Mr.  W.  H.  Howell,  Fellow  of  the  Johns  Hopkins  Uni- 
versity, who  has  corrected  most  of  the  proof-sheets,  and 
prepared  the  index. 

H.  NEWELL  MABTLKT. 

JOHNS  HOPKINS  UNIVERSITY, 

August  10,  1883. 


PREFACE  TO  THE  SECOND  EDITION. 


THE  second  edition  of  this  book  differ?  from  the  first  for 
the  most  part  only  in  verbal  alterations  or  typographical 
corrections.  Chapter  XXIII. ,  however,  is  entirely  new, 
and  deals  in  some  detail  with  the  important  question  of 
the  influence  on  health  of  alcohol  and  various  narcotics. 

H.  N.  M- 

March  26,  1864. 


CONTENTS. 


CHAPTER  I. 

THE  GENERAL  STRUCTURE  AND  ARRANGEMENT   OF  THE   HUMAN 

BODY. 

PAGE 

Human  Physiology — Hygiene — Anatomy — Histology — Tissues — 
Organs — The  general  plau  on  which  the  body  is  constructed 
— Man  is  a  vertebrate  animal — The  two  chief  cavities  of  the 
body — The  limbs — Man's  place  among  vertebrates—Sum- 
mary   1 

CHAPTER  II. 

THE  SfrCROSCOPICAL   AND   CHEMICAL,   COMPOSITION    OF    THE   BODY. 

What  the  tissues  are  like — Cells  and  fibres — The  physiological 
division  of  labor  and  its  results — The  chemical  composition 
of  the  body — Albumens,  fats,  and  carbohydrates 15 

CHAPTER  III. 

THE     SKELETON. 

Bone,  cartilage,  and  connective  tissue— Articulations  and  joints 
— The  bony  skeleton — Uses  of  the  mode  of  structure  of  the 
spinal  column — Comparison  of  the  skeletons  of  the  upper 
and  lower  limbs — Peculiarities  of  the  human  skeleton 23 

CHAPTER  IV. 

THE   STRUCTURE,    COMPOSITION,    AND   HYGIENE   OF   BONES. 

Gross  structure  of  bones — The  humerus — Why  many  bones  are 
hollow — Histology  of  bone — Chemical  composition  of  bone 
-Hygiene  of  the  bony  skeleton — Fractures 47 


CONTENTS. 
CHAPTER  V. 

JOINTS. 

PAGE 

Muscles  and  joints — Structure  of  the  hip  joint — Ball  and  socket 
joints — Hinge  joints — Pivot  joints — Gliding  joints— Disloca- 
tions— Sprains * 59 

CHAPTER  VI. 

THE   MUSCLES. 

The  parts  of  a  muscle — The  origin  and  insertion  of  muscles — 
Varieties  of  muscles — How  muscles  are  controlled— Gross 
structure  of  a  muscle — Histology  of  muscle — Plain  muscular 
tissue — The  muscular  tissue  of  the  heart — The  chemical 
composition  of  muscle — Beef  tea  and  meat  extracts 67 

CHAPTER  VII. 

MOTION  AND  LOCOMOTION. 

The  special  physiology  of  muscles — Levers  in  the  body — Pulleys  \ 
in  the  body — Standing — Walking — Running — Hygiene  of  ] 
the  muscles — Exercise 80 

CHAPTER  VIII. 

WHY  WE  EAT  AND  BREATHE. 

How  it  is  that  the  body  can  do  work — The  conservation  of  en- 
ergy— Illustrations — Why  we  need  food — Why  the  body  is 
warm — The  influence  of  starvation  upon  muscular  work  and 
animal  heat — Oxidations  in  the  body — The  oxygen  food  of 
the  body — Appendix 93 

CHAPTER  IX. 

. NUTRITION. 

The  wastes  of  the  body — Receptive  and  excretory  organs — The 
•    organs  and  processes  concerned  in  nutrition 105 

CHAPTER  X. 

POODS. 

Foods  as  tissue  formers — What  foods  must  contain — The  special 
importance  of  albuminous  foods — The  dependence  of  animals 


CONTENTS.  IX 

PAGK 

on  plants— Non-oxidizable  foods— Definition  of  foods— All 
mentary  principles — The  nutritive  value  of  various  foods — 
Alcobol— Tea  and  coffee— Cooking— The  advantages  of  a 
mixed  diet 110 

CHAPTER  XL 

THE   DIGESTIVE   ORGANS. 

General  arrangement  of  the  alimentary  canal— Glands — The 
mouth — The  teeth — Hygiene  of  the  teeth— The  tongue — A 
furred  tongue — The  salivary  glands — The  tonsils — The 
pharynx — The  gullet — The  stomach — Palpitation  of  the 
heart — The  small  intestine — The  large  intestine— The  liver 
—The  pancreas 128 

CHAPTER  XII. 

» 

DIGESTION. 

The  object  of  digestion — Uses  of  saliva— Swallowing— The  gas- 
tric juice — Chyme — Chyle — The  pancreatic  secretion — The 
bile  and  its  uses — The  intestinal  secretions — Indigestible  sub- 
stances— Dyspepsia — Appetite — Absorption  from  the  ali- 
mentary canal — The  lacteals — Appendix 152 

CHAPTER  XIII. 

BLOOD   AND   LYMPH. 

Why  we  need  blood— Histology  of  blood — The  blood  corpuscles 
— Hgeniaglobin — The  coagulation  of  blood — Uses  of  coagu- 
lation— Blood  serum — Blood  gases  —  Summary — Hygienic 
remarks — Quantity  of  blood  in  the  body — The  lymph — 
Dialysis — The  lymphatic  or  absorbent  vessels — Summary — 
Appendix 174 

CHAPTER  XIV. 

THE  ANATOMY  OP    THE   CIRCULATORY  ORGANS. 

The  organs  of  circulation — Functions  of  the  main  parts  of  the 
vascular  system — The  pericardium — The  heart — The  vessels 
connected  with  the  heart — How  the  heart  is  nourished — 
The  valves  of  the  heart-1— The  main  arteries  of  the  body — 
The  properties  of  the  arteries — The  capillaries — The  veins 
— The  course  of  the  blood — The  portal  circulation — Arterial 
and  venous  blood — Appendix 192 


X  CONTENTS. 

CHAPTER  XV. 

THE   WORKING   OP   THE   HEART   AND   BLOOD  VESSELS. 

PAGE 

The  beat  of  the  heart — Events  occurring  in  each  beat — Use  of  the 
papillary  muscles— Sounds  of  the  heart — Function  of  the 
auricles — Work  done  daily  by  the  heart — The  pulse — Blood- 
flow  in  capillaries  and  veins — Why  there  is  no  pulse  in  these 
vessels — The  muscles  of  the  arteries — Taking  cold — Bathing 
—Appendix 216 

CHAPTER  XVI. 

THE    OBJECT   AND   THE   MECHANICS   OF   RESPIRATION. 

The  object  of  respiration  —  The  respiratory  apparatus — The 
windpipe — Bronchitis — The  lungs— The  pleura — Pleurisy 
— Why  the  lungs  remain  expanded — How  the  air  is  renewed 
in  the  lungs — The  respiratory  movements — The  respiratory 
soundj> — Hygienic  remarks— Appendix , 233 

CHAPTER  XVII. 

THE   CHFMISTRY   OF   RESPIRATION   AND   VENTILATION. 

The  quantity  of  air  breathed  daily — Changes  produced  in  the  air 
by  being  breathed — Ventilation — When  breathed  air  be- 
comes unwholesome — How  to  ventilate — Changes  under- 
gone by  the  blood  in  the  lungs — Appendix 250 

CHAPTER    XVIII. 

THE   KIDNEYS   AND   THE   SKIN. 

General  arrangement  of  the  nitrogen-excreting  organs— Gross 
structure  of  the  kidney — Histology  of  the  kidney — The 
renal  secretion — The  skin — Hairs — Nails — The  sweat  glands 
—The  sebaceous  glands — Hygiene  of  the  skin — Bathing — 
Appendix 261 

CHAPTER  XIX. 

WHY  WE  NEED  A  NERVOUS  SYSTEM — ITS  ANATOMY. 

The  harmonious  co-operation  of  the  organs  of  the  body — Co- 
ordination— Nerve  trunks  and  nerve  centres — The  Of 
spinal  centre — The  spinal  cord — The  brain — The    cranial 
nerves — The  sympathetic  nervous  system — The  histology  of 
nerve  centres  and  nerve  trunks — Appendix , 279 


CONTENTS.  XI 

CHAPTER  XX. 

THE   GENERAL  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM. 

PAGE 

The  properties  of  the  nervous  system — Functions  of  nerve 
centres  and  nerve  trunks — Sensory  and  motor  nerves — Classi- 
fication of  nerve  centres — Functions  of  the  cerehrum — Of 
the  cerebellum — Reflex  nerve  centres — Automatic  nerve 
centres — Habits — Hygiene  of  the  brain — Appendix 301 

CHAPTER  XXI. 

THE  SENSES. 

Common  sensation  and  special  senses—  Hunger  and  thirst — The 
visual  apparatus  and  its  appendages — The  globe  of  the  eye 
— The  retina — The  blind  spot — The  formation  of  images  on 
the  retina — Short  sight  and  long  sight — Hygiene  of  the  eyes 
— Hearing — The  tympanum — The  internal  ear — Touch — 
The  localization  of  skin  sensations — The  temperature  sense 
—Smell— Taste 314 

CHAPTER  XXII. 

VOICE    AND    SPEECH. 

The  production  of  voice — The  pitch  of  the  voice — Speech — 
Structure  of  the  larynx— The  vocal  chords — Range  of  the 
human  voice — Vowels— Semi-vowels — Consonants 335 

CHAPTER    XXIII. 

ALCOHOL  AND  OTHER  STIMULANTS  AND  NARCOTICS. 

Introductory — Is  alcohol  a  food? — Composition  and  properties 
of  alcohol — Alcoholic  beverages — The  direct  physiological 
action  of  pure  alcohol — Action  of  diluted  alcohol — Absorp- 
tion of  alcohol — Primary  effects  of  a  moderate  dose  of 
alcohol — Secondary  effects  of  alcohol — Minor  diseased  con- 
ditions produced  by  alcohol — Acute  alcoholic  diseases — 
Delirium  tremens — Dipsomania — Chronic  alcoholic  diseases 
— Deteriorations  of  tissue  due  to  alcohol — Organs  impaired 
or  destroyed  by  alcohol — Moral  deterioration  produced  by 
alcohol — Opium  and  morphia — Chloral — Tobacco 343 


THE    HUMAN    BODY, 


CHAPTER    L 

THE   GENERAL    STRUCTURE    AND    ARRANGEMENT    OF 
THE   HUMAN    BODY. 

Human  Physiology  is  that  department  of  science 
which  has  for  its  object  the  discovery  and  accurate  de- 
scription of  the  properties  and  actions  of  the  living 
healthy  human  body,  and  the  detection  of  the  uses  or 
(as  physiologists  call  them)  the  functions,  j?f  its  various 
parts.  Physiologists  endeavor  to  find  out  what  the 
body,  as  a  whole,  does  while  alive,  and  what  each  part  of 
it  does,  and  how  it  does  it ;  also  under  what  conditions 
the  work  of  the  body  is  best  performed  ;  and,  in  connec- 
tion with  this  last  aim,  to  furnish  the  basis  of  Hygiene, 
the  science  which  is  concerned  with  the  laws  and  condi- 
tions of  health. 

T;at  is  human  physiology?     What  is  a  function?    What  do 
physiologists  endeavor  to  discover?     What  is  meant  by  Hygiene  ? 
1 


2  THE    HUMAN   BODY. 

Anatomy. — Clearly,  the  first  step  to  be  taken  towards 
finding  out  the  use  and  mode  of  working  of  each  part 
of  the  body  is  to  find  out  what  the  parts  are  ;  this  study 
is  known  as  Human  Anatomy.  Examined  merely  from 
the  exterior,  the  body  is  quite  a  complicated  structure  : 
we  can  all  see  for  ourselves,  head  and  neck,  trunk  and 
limbs,  and  even  many  smaller  but  quite  distinct  parts 
entering  into  the  formation  of  these  larger  ones,  as  eyes, 
nose,  ears,  and  mouth ;  arm,  forearm,  and  hand  ;  thigh, 
leg,  and  foot.  This  knowledge  of  its  complexity,  which 
we  may  all  arrive  at  by  looking  en  the  outside  of  the  body, 
is  vastly  extended  when  it  is  dissected  and  its  interior 
examined  ;  we  then  learn  that  it  is  made  up  of  many 
hundreds  of  diverse  parts,  each  having  its  own  structure, 
and  form,  and  purpose,  but  all  harmoniously  working 
together  in  health. 

Summary. — Anatomy  is  concerned  with  the  form  and 
structure  and  connections  of  the  parts  of  the  body. 
Physiology  with  the  uses  of  the  parts,  and  the  ways  in 
which  they  work.  Hygiene  with  the  conditions  of  life 
which  promote  the  health  of  the  body. 

Microscopic  Anatomy  or  Histology. — When  we  exam- 
ine the  body  from  its  exterior,  we  observe  that  a  number 
of  different  materials  enter  into  its  formation.  Hairs, 
nails,  skin,  and  teeth  are  quite  different  substances  ;  by 
feeling  through  the  skin  we  find  harder  and  softer  solid 

What  is  human  anatomy  ?  Give  illustrations  of  the  complexity 
of  the  body  in  structure?  Is  its  internal  structure  as  varied  as  its 
external? 

State  in  a  few  words  the  subject  matters  of  the  sciences  of  Human 
Anatomy,  Physiology,  and  Hygiene. 

Give  examples  of  the  variety  of  substances  entering  into  the  com- 
position of  the  body.  What  may  we  feel  through  the  skin  ? 


MICROSCOPIC1    ANATOMY    OR    HISTOLOGY.  3 

masses  under  it ;  while  the  blood  which  flows  from  a  cut 
finger,  and  the  saliva  which  moistens  the  mouth,  show 
clearly  that  liquids  exist  in  the  body. 

If  we  were  to  go  farther  and  examine  closely,  outside 
and  inside,  any  one  part  of  the  body,  the  hand  for  in- 
stance, we  should  find  it  made  up  of  quite  a  number  of 
different  materials.  On  its  exterior  we  see  skin  and 
nails  ;  if  the  skin  were  dissected  off  we  should  find  under 
it,  more  or  less  yellowish-white/^;  beneath  the  fat  would 
lie  a  number  of  red  soft  masses,  the  muscles  (answering  to 
what  we  call  the  lean  of  meat)  ;  under  the  muscles,  again, 
would  be  hard,  rigid,  whitish  bones  ;  at  the  finger  joints, 
where  the  ends  of  different  bones  lie  close  together,  we 
should  find  them  covered  by  still  another  substance,  gristle 
or  cartilage.  Finally,  binding  skin  and  fat  and  muscles 
and  bone  together, we  should  discover  a  tough  stringy  mate- 
rial, quite  different  from  all  of  them,  arid  which,  since  it 
unites  all  the  rest,  is  called  connective  tissue.  If  we  took 
any  other  portion  of  the  body  we  should  arrive  at  a  similar 
result ;  it,  too,  would  be  made  up  of  a  number  of  different 
materials,  which  materials  might,  as  in  the  case  of  the 
foot,  be  identical  with  those  found  in  the  hand  but  ar- 
ranged together  in  a  different  way  so  as  to  perform  another 
function  (just  as  wood  and  nails  may  be  used  to  build  a 
house  or  a  bridge,  but  are  put  together  in  a  different 
manner  in  the  two  cases);  or  we  might,  as  in  the  eye,  find 
in  addition  to  some  materials  found  in  the  hand  others 
quite  unlike  any  of  them. 

What  different  materials  do  we  see  on  looking  at  a  hand? 
What  others  would  be  found  on  dissecting;  away  the  skin?  What 
is  the  technical  name  for  the  lean  of  meat  ?  What  is  the  technical 
name  of  gristle?  What  is  connective  tissue?  Are  other  parts  of  the 
body  besides  the  hand  made  up  of  different  substances  ?  Illustrate 
by  an  example? 


4  THE    HITMAN   BODY. 

The  branch  of  anatomy  which  deals  with  the  charac- 
ters of  the  materials  used  in  the  construction  of  the  parts 
of  the  body  is  called  histology,  or,  since  it  is  mainly  carried 
on  with  the  aid  of  the  microscope,  microscopic  anatomy. 

Tissues. — Each  of  the  different  primary  building  ma- 
terials which  can  be  distinguished,  either  with  or  without 
the  microscope,  as  entering  into  the  construction  of  the 
body,  is  called  a  tissue  ;  we  speak,  for  example,  of  muscu- 
lar tissue,  fatty  tissue,  bony  tissue,  cartilaginous  tissue, 
and  so  forth  ;  each  tissue  has  certain  properties  in  which 
it  differs  from  all  the  rest,  and  which  it  presents  in  what- 
ever part  of  the  body  it  may  be  found.  It  also  is  charac- 
terized by  certain  appearances  when'  examined  with  a  mi- 
croscope, which  are  the  same  for  the  same  tissue  no  matter 
where  it  is  found.  The  total  number  of  important  tissues 
is  not  great ;  the  variety  in  structure  and  use  which  we 
find  in  the  parts  of  the  body  depends  mainly  on  the 
diverse  ways  in  which  the  same  tissues  are  combined 
together,  over  and  over  again,  in  different  parts. 

Organs. — A  portion  of  the  body  composed  of  several 
tissues,  and  specially  fitted  for  the  performance  of  a  par- 
ticular duty  or  function,  is  called  an  organ  ;  thus,  the  hand 
is  an  organ  of  prehension  ;  the  eye,  the  organ  of  sight  ; 
the  stomach,  an  organ  of  digestion ;  and  so  forth. 

Summary. — The  human  body  is  made  up  of  a  limited 
number  of  tissues  ;*  each  tissue  has  a  characteristic  ap- 

What  is  histology?     Give  another  name  for  it. 

What  is  a  tissue?  Give  examples.  How  do  tissues  differ?  Are 
there  a  large  number  of  important  tissues?  How  is  the  variety  in 
structure  of  the  parts  of  the  body  produced? 

What  is  an  organ?  Give  examples.  Of  what  is  the  body  made 
up  ? 

*  The  various  tissues  of  the  body  will  be  considered  in  more  detail  subsequently:         ^ 
the  more  important  are — 1.  Bony  tissue.    3.  Cartilaginous  tissue.    3.  White  fibroua        i 


TISSUES    AND    ORGAN'S.  5 

pearance,  by  which  it  can  be  recognized  with  the  micro- 
scope, and  some  one  or  more  distinctive  properties  which 
fit  it  for  some  special  use  ;  thus,  it  may  be  very  tough,  and 
suited  for  binding  other  parts  together  ;  or  rigid,  and 
adapted  to  preserve  the  shape  of  the  body  ;  or  have  the 
power  of  changing  its  length  and  be  useful  for  moving 
parts  to  which  its  ends  are  attached. 

The  tissues  are  variously  combined  to  form  the  organs 
of  the  body,  of  which  there  are  very  many,  differing  in  size, 
shape,  and  structure  ;  some  organs  contain  only  a  few  tis- 
sues ;  others,  a  great  many  ;  some  possess  only  tissues 
which  are  found  also  in  other  organs,  others  contain  one 
or  more  tissues  peculiar  to  themselves  ;  but  wherever  an 
organ  is  found,  it  is  constructed  and  placed  with  reference 
to  the  performance  of  some  duty  ;  the  organs  are  the  ma- 
chines which  are  found  in  the  factory  represented  by  the 
body,  and  the  tissues  are  the  materials  used  in  building 
the  machines;  or,  using  another  illustration,  we  may,  with 
Longfellow,  compare  the  body  to  a  dwelling-house  ;  and 
then  go  on  to  liken  the  tissues  to  the  brick,  stone,  mortar, 
wood,  iron,  and  glass,  used  in  building  it;  and  the  organs 
to  the  walls,  floors,  ceilings,  doors,  and  windows,  which, 
made  by  combining  the  primary  building  materials  in 
different  ways,  have  each  a  purpose  of  their  own,  and  all 
together  make  the  house. 

How  are  tissues  recognized  ?  Give  examples  of  differences  in 
properties  of  various  tissues. 

How  do  organs  differ  from  one  another  ?  In  wliat  do  all  organs 
agree  ?  Illustrate  the  relation  of  organs  and  tissues  to  the  body  as  a 
whole  ? 


connective  tissue.  4.  Yellow  elastic  tissue.  5.  Glandular  tissue,  of  which  there  are 
many  varieties.  6.  Respiratory  tissues.  7.  Fatty  tissue.  8.  Sense-organ  or  irritable 
V.esues.  9.  Nerve  cell  tissue.  10.  Nerve  fiber  tissue.  11.  Striped  muscular  tissue. 
12.  Unstriped  muscular  tissue.  13.  Epidermic  and  epithelial  tissue. 


6  THE    HUMAN    BODY. 

The  general  plan  on  which,  the  Body  is  constructed. — 
When  we  desire  to  gain  a  general  idea  of  the  structural 
plan  of  any  object  we  examine,  if  possible,  sections  made 
through  it  in  different  directions  ;  the  botanist  cuts  the 
stem  of  the  plant  he  is  examining  lengthwise  and  cross- 
wise, and  studies  the  surfaces  thus  laid  bare  ;  a  geologist, 
investigating  the  structure  of  any  portion  of  the  earth's 
crust,  endeavors  to  find  exposed  surfaces  in  canons,  in 
railway  cuttings,  and  so  forth,  where  he  may  see  the  strata 
exposed  in  their  natural  relative  positions  ;  and  the  archi- 
tect draws  plans  which  show  to  his  clients  sections  of  the 
building  which  he  proposes  to  erect  for  them  ;  so,  also,  the 
best  method  of  getting  a  good  general  idea  of  the  way  in 
which  the  parts  of  the  human  body  are  put  together  is 
to  study  them  as  laid  bare  by  cuts  made  in  different  direc- 
tions ;  this  gives  us  a  general  outline  and  the  details  may 
be  filled  in  afterwards. 

If  the  whole  body  were  divided  from  the  crown  of 
the  head  to  the  lower  end  of  the  trunk,  and  exactly  in  the 
middle  line,  so  as  to  separate  it  into  right  and  left  halves, 
we  should  see  something  like  Fig.  1,  if  we  looked  at  the  cut 
surface  of  the  right  half.  Such  a  section  shows  us,  first, 
that  the  body  fundamentally  consists  of  two  tubes  or  cav- 
ities, separated  by  a  solid  bony  partition.  The  larger  cav- 
ity, I,  c,  known  as  the  ventral  or  licemal  cavity,  lies  on 
the  front  side,  and  contains  the  greater  part  of  the  organs 

How  do  we  start  by  preference  to  gain  a  knowledge  of  the  struc- 
tural plan  of  any  mass  of  matter?  Give  examples.  Apply  to 
the  study  of  human  anatomy. 

What  should  we  see  on  examining  the  cut  surface  of  a  human 
body  divided  into  right  and  left  halves?  What  organs  lie  in  the 
haemal  cavity?  What  in  the  neural?  How  far  does  the  haemal 
cavity  extend  toward  the  head  ? 


GENERAL    PLAN    OF    BODY. 


concerned  in  keeping  up  the 
blood  flow  (organs  of  circula- 
tion), in  breathing  (organs  of 
respiration)  and  in  digesting 
food  (organs  of  digestion).  It 
does  not  reach  up  into  the  neck, 
but  is  entirely  confined  to  the 
trunk.  The  smaller  cavity,  a, 
a',  is  tubular  in  the  trunk  region, 
but  passes  on  through  the  neck, 
and  widens  out  in  the  skull ;  it 
is  known  as  the  dorsal  or  neural 
cavity,  and  contains  the  most 
important  nervous  organs,  the 
brain,  N',  and  spinal  cord,  N. 
In  the  partition  between  the  two 
cavities  is  a  stout  bony  column, 
the  backbone  or  spine,  e,  e, 
which  is  made  up  of  a  number  of 
short  thick  bones  piled  one  on 
the  top  of  another. 

Man  is  a  vertebrate  animal. 
— The  presence  of  these  two 
chambers  with  the  solid  par- 
tition between  them  is  a  prim- 
ary fact  in  the  anatomy  of 
the  body  ;  it  shows  that  man  is 
a  vertebrate  animal,  that  is  to 
say,  is  a  back-boned  animal, 
and  belongs  to  the  same  great 

What  lies  between  the  haemal  and 
neural  cavities?  Of  what  is  the  spine 
composed  ? 


Fia.  1. — Diagrammatic  longitud- 
inal section  of  the  body.  «,  the 
neural  tube,  with  its  upper  enlarge- 
ment in  the  skull  cavity  at  a';  N, 
the  spinal  cord;  N',  the  brain;  ee, 
vertebrae  forming  the  solid  parti* 
tion  between  the  dorsal  and  vent- 
ral cavities;  5,  the  pleura!,  and,  e, 
the  abdominal  division  of  the 
ventral  cavity,  separated  from  one 
another  by  the  diaphragm,  'd;  i, 
the  nasal,  and  o.  the  mouth  cham- 
ber, opening  behind  into  the 
pharynx,  from  which  one  tube 
leads  to  the  lungs,  /,  and  another 
to  the  stomach,/;  A,  the  heart;  k, 
a  kidney  ;  s,  the  sympathetic 
nervous  chain.  From  the  stomach, 
f.  the  intestinal  tube  leads  through 
the  abdominal  cavity  to  the  pos- 
terior opening  of  the  alimentary 
canal, 


8  THE    HUMAN    BODY. 

group  as  fishes,  reptiles,  birds,  and  beasts*  :  sea  ane- 
mones, clams,  and  insects  are  invertebrate  animals,  and 
built  on  quite  different  plans ;  sections  made  through 
any  of  them  from  the  head  to  the  opposite  end,  would 
show  nothing  like  those  two  main  cavities  with  a  backbone 
between  them  which  exist  in  our  own  bodies. 

Contents  of  the  two  chief  cavities  of  the  body. — Exam- 
ination of  Fig.  1  shows  that  the  ventral  cavity  is  entirely 
closed  itself,  though  some  things  which  lie  in  it  are  hollow 
and  communicate  with  the  exterior.  On  the  head  we 
find  the  nose,  i,  and  the  mouth,  o,  opening  on  the  ven- 
tral side ;  that  is  on  that  surface  of  the  body  next  which 
the  haemal  cavity  lies.  The  nose  chamber  joins  the  mouth 
chamber  at  the  throat,  and  from  the  throat  two  tubes 
run  down  through  the  neck  and  enter  the  ventral  cavity. 
One  of  these  tubes,  placed  on  the  ventral  side  of  the  other, 
is  the  windpipe,  and  leads  to  the  lungs,  I;  the  other  is  the 
gullet,  and  leads  to  the  stomach,  f.  From  the  stomach, 
another  tube,  the  intestine,  leads  to  the  outside  again  at 
the  lower  or  posterior  f  end  of  the  trunk.  Mouth,  throat, 

What  fact  in  man's  anatomy  makes  him  a  vertebrate  animal? 
Name  some  other  vertebrate  animals.  Name  some  invertebrates. 
How  would  sections  made  through  invertebrates  differ  essentially 
from  similar  sections  made  through  a  man? 

Is  the  ventral  cavity  open?  Do  any  smaller  cavities  in  it  open  on 
the  exterior  of  the  body?  What  openings  do  we  rind  on  the  head? 
What  is  the  windpipe?  To  where  does  it  lead?  What  is  the  intes- 
tine? What  parts  constitute  the  alimentary  canal?  Does  this  canal 
lie  entirely  within  the  haemal  cavity? 

*  The  main  groups  m  which  animals  arc  arranged  are—  1.  Vertebrata,  or  backboned 
animals.  2.  Mollusca,  including  snails,  slugs,  clams,  oysters.  &c.  3.  Arthropoda, 
including  flies,  moths,  beetles,  centipedes,  lobsters,  spiders,  &c.  4.  Vermes,  includ- 
ing worms  of  various  kinds.  5.  Echinodermata  (hedgehog-skinned  animals),  in- 
cluding sea  urchins,  star  fishes,  &c.  6.  Cailenterala,  the  sea-anemones  and  their 
allies.  7.  The  Protozoa  ;  all  microscopic  and  very  simple  in  structure. 

t  In  anatomy  the  head  end  of  an  animal  is  spoken  of  as  anterior,  and  the  oppo- 
site end  as  posterior,  no  matter  what  may  be  the  natural  standing  position  of  the 
creature, 


TWO     CHIEF    CAVITIES    OF   THE    BODY.  9 

gullet,  stomach,  and  intestine,  together  form  the  aliment- 
ary canal,  which,  as  we  see,  begins  ~on  the  head  quite 
above  or  anterior  to  the  ventral  cavity ;  then,  at  the  bot- 
tom of  the  neck,  enters  the  ventral  cavity  and  runs  on 
through  it,  to  pass  out  again  posteriorly;  just  as  a  tube 
might  pass  quite  through  a  box,  in  at  one  end  and  out  at 
the  other,  without  opening  into  it  at  all.  In  addition  to 
the  lungs  and  the  greater  part  of  the  alimentary  canal, 
the  ventral  cavity  contains  several  other  things  of  which 
we  shall  have  more  to  say  presently  ;  among  the  more 
important  of  them  are,  the  heart,  h  ;  the  kidneys,  k  ;  the 
sympathetic  nerve  centers,  s;  and  several  large  organs 
making  juices  which  are  conveyed  by  tubes  into  the  ali- 
mentary canal  and  assist  in  digesting  our  food. 


FIG.  2.— A  diagrammatic  section  across  the  body  in  the  chest  region,  x,  the  dorsal 
tube,  which  contains  the  spinal  cord;  the  l>lack  mass  surrounding  it  is  a  vertebra; 
a,  the  gul lot.  a.  part  of  the  alimentary  canal;  h,  the  heart;  sy,  sympathetic  nervous 
system;  II.  lungs;  the  dotted  lines  around  them  are  the  pleurae;  rr,  ribs;  tl,  the 
breastbone. 

If  we  examined  a  section  made  across  the  trunk  of  the 
body,  say  about  the  level  of  the  middle  of  the  chest  (Fig. 
2),  we  would  find,  on  the  dorsal  side,  the  neural  tube,  x, 
cut  across,  and  in  it  the  spinal  cord,  which  is  not  repre- 

Name  some  organs,  in  addition  to  parts  of  the  alimentary  canal, 
which  are  found  in  the  ventral  cavity.  Describe  what  would  he 
seen  on  a  section  oiade  across  the  hody  ahout  tfte  middle  of  tb$ 
chest, 


10  THE    HUMAN   BOD7. 

sented  in  the  figure.  The  thick  black  mass  below  the 
neural  tube  is  part  of  the  spinal  column  ;  bounded  by  this 
dorsally,  by  a  rib,  r,  r,  on  each  side,  and  by  the  breastbone, 
sty  on  the  ventral  side  (below  in  the  figure)  is  the  haemal 
cavity,  containing  the  lungs,  Z,  I ;  the  heart,  h;  the  gul- 
let, a;  and  the  sympathetic  centers,  sy. 


FIG.  3.— A  section  across  the  forearm  a  short  distance  below  the  elbow-joint.  1 
and  17,  its  two  supporting  bones,  the  radius  and  ulna;  e,  the  epidermis  and  d,  the 
dennis,  of  the  skin;  the  latter  is  continuous  below  with  bands  of  connective  tissue, 
«,  which  penetrate  between  and  invest  the  muscles,  which  are  indicated  by  numbers, 
n,  ft,  nerves  and  vessels. 

The  Limbs. — If,  instead  of  the  trunk  of  the  body,  our 
section  were  made  across  one  of  the  limbs,  we  should  find 
no  such  arrangement  of  cavities  on  each  side  of  a  bony 
axis.  The  limbs  have  a  supporting  axis  made  of  one  or 
more  bones  (as  seen  at  Z7and  R,  Fig.  3,  which  represents 
a  section  made  across  the  forearm  near  the  elbow  joint), 
but  around  this  axis  soft  parts,  chiefly  muscles,  are  closely 
packed  ;  and  the  whole,  like  the  trunk,  is  enveloped  by 
skin.  The  only  cavities  in  the  limbs  are  branching  tubes, 
which  are  filled  during  life  either  with  Uood,  or  a  watery- 
looking  liquid  known  as  lymph.  These  tubes,  the  Uood 
and  lympJi  vessels  respectively,  are  not,  however,  character- 
istic of  the  limbs,  for  they  also  exist  in  abundance  in  head, 
neck  and  trunk. 

How  do  the  limbs  differ  from  the  trunk?  How  is  each  limb 
supported?  Describe  the  parts  exposed  on  a  cross  section  of  the 
forearm?  What  cavities  exist  in  a  limb?  What  do  they  contain? 
Are  they  f ound  iu  otJier  par;  *  ui  w«  body  2 


MAN'S    PLACE    AMONG     VERTEBRATES.  \\ 

Man's  place  among  Vertebrates. — It  must  be  clear  to 
every  one  that  although  man's  structural  plan  in  its  broad 
features,  simply  indicates  that  he  is  a  vertebrate  animal, 
yet  he  is  much  more  like  some  vertebrates  than  others. 
The  hair  covering  more  or  less  of  his  body,  and  the  organs 
which  produce  milk  for  the  nourishment  of  the  infant  by 
its  mother,  are  absent  entirely  in  fishes,  reptiles,  and  birds, 
but  are  possessed  by  ordinary  four-footed  beasts  and  by 
whales,  bats,  arid  monkeys.  The  organs  which  form  milk 
are  the  mammary  glands,  and  all  kinds  of  animals  whose 
'  males  possess  them  are  known  as  Mammalia  *:  man  is, 
therefore,  a  Mammal.  In  internal  structure  one  of  the 
nost  important  characters  of  the  Mammalia  is  the  pres- 
ence of  a  cross-partition,  called  the  midriff  or  die- 
phragm,  which  separates  the  haemal  cavity  into  an  an- 
terior and  a  posterior  division.  This  partition  is  shown  at 
d  in  Fig.  1,  where  it  is  seen  to  divide  the  ventral  cavity 
into  an  upper  and  a  lower  story ;  the  upper  or  anterior  is 
the  -chest  or  thorax  cavity;  the  lower  or  posterior,  the 
abdominal  cavity.  The  chest  contains  the  heart,  lungs, 
and  most  of  the  gullet ;  the  abdomen  contains  tht,  lower 

In  what  external  characters  does  the  human  body  differ  from 
that  of  fishes,  reptiles,  and  birds?  Name  some  animals  which  agree 
with  mankind  in  the  possession  of  these  characters  ?  \Vhat  are 
the  mammary  glands?  What  is  meant  by  Mammalia?  To  what  di- 
vision of  vertebrate  animals  does  man  belong? 

Point  out  a  fact  in  internal  structure  in  which  the  Mammalia 
differ  from  other  vertebrates?    Where  does  the  diaphragm  lie?    What      , 
is  the  name  of  the  cavity  above  it?     What  is  the  name  of  the  cavity      , 
below  it?    Name  some  organs  lying  in  the  thorax.      Some  placed  in 
the  abdomen.     Some  which  run  through  both. 

— —  .to- 

*  Zoologists  classify  vertebrate  animals  in  five  groups.    1.  Pisces,  including  all  -"to 
"|  sharks,  eels,  salmons,  shad,  perch,  &c.,  but  excluding  the  so-called 
'"*  Meters,  which  are  not  vertebrates  at  all.    2.  Am- 
]<-i-3  &c.  3.  ReptUia,  lizards,  alligato>--  "••-«-' 


THE    HUMAN   BODY. 


ind  of  the  gullet  (which  pierces  the  diaphragm),  the 
itomach,  the  intestine,  the  kidneys,  and  most  of  the 
/organs  making  digestive  liquids.  The  sympathetic  nerve 


(~ 


13 

no 


Fro.  4.— The  body  opened  from  the  front  to 
biipavity.  tu.  lungs;  A,  heart,  partly  covered  by  o 
/^..'Aafcrjflbep  respectively:  ma,  stomach;  ne,  the  g4 
A  ^^ff^h  hanes  down  from  the  oosf prior  1>1 

ja.rc  iiiey  it 


Il 

^r 
they  COlitUUlf 


ZOOLOGICAL    POSITION   OF    MAN.  13 

centers  run  through  both  abdomen  and  chest,  and  extend 
beyond  the  latter  into  the  neck. 

The  ventral  cavity,  opened  from  the  front,  but  with  its 
contents  undisturbed,  is  shown  in  figure  4  We  there  see 
the  edge  of  the  diaphragm,  2,  2 ;  above  this,  in  the  chest, 
the  lungs,  lu,  lu,  and  the  heart,  h  ;  the  latter  partly  covered 
by  other  things.  Below  the  diaphragm  is  the  abdominal 
cavity,  containing  in  its  upper  part  the  liver,  le,  le'\  the 
stomach,  ma  ;  and  the  spleen,  mi\  hanging  down  like  an 
apron  from  the  lower  border  of  the  stomach  is  the  amen- 
tum, ne,  ne,  which  lies  over  and  conceals  the  intestines. 

Summary. — Man  is  a  vertebrate  animal,  because  his 
body  presents  dorsal  and  ventral  cavities  separated  from 
one  another  by  a  hard  partition  ;  the  dorsal  cavity  con- 
tains the  brain  and  spinal  cord,  and  reaches  into  the  head; 
the  ventral  cavity  stops  at  the  bottom  of  the  neck  and 
contains  the  main  organs  of  circulation,  respiration,  and 
digestion. 

Man  belongs  to  that  subdivision  of  vertebrates  known 
as  Mammalia  (1)  because  more  or  less  of  his  surface  is 
covered  by  hair  ;  (2)  because  of  the  presence  of  mammary 
glands  ;  (3)  because  the  ventral  cavity  is  completely  sep- 
arated by  the  diaphragm  into  thorax  and  abdomen. 

That  man  is  intellectually  incomparably  superior  to 
any  other  animal,  and  stands  supreme  in  the  world,  can 


Name  the  parts  seen  when  the  front  wall  of  a  man's  trunk  is  cut 
away.  Describe  the  relative  positions  of  these  parts. 

On  what  anatomical  grounds  do  we  call  man  a  vertebrate  animal? 
What  lies  in  the  dorsal  or  neural  cavity?  How  far  does  the  upper  end 
of  this  cavity  reach?  What  organs  lie  in  the  ventral  cavity?  Where 
does  its  uppti^. limit  lie?  TV  hy  is  man  a  Mammal?  in  what  is  man 
superior  to  iy  other  animal?  From  what  point  of  view  have  anato- 
mists to  regard  man's  body?  What  sort  of  facts  do  they  take  iii to 
account  in  assigning  man's  position  among  animals? 


14  THE    HUMAN   BODY. 

be  doubted  by  no  one  ;  still  greater  is  his  supremacy  when 
we  consider  his  power  of  forming  conceptions  of  right  and 
wrong,  and  his  knowledge  of  moral  responsibility;  But 
anatomists  have  only  to  deal  with  man's  body  as  a  mate- 
rial object,  and  as  such  they  classify  it  among  other  ani- 
mal bodies  according  to  the  greater  or  less  resemblances 
or  differences  which  are  found  between  it  and  them.  * 


*  It  will  be  found  very  useful  to  accompany  the  teaching  of  this  chapter  with  a 
demonstration  on  the  body  of  a  dead  rat,  kitten,  or  puppy.  On  opening  the  body 
the  chest  and  abdominal  cavities  will  be  readily  shown,  and  also  the  main  organs 
in  them.  Then,  on  opening  the  skull,  the  brain  will  be  seen,  and  on  cutting  across 
the  spinal  column  with  stron£  scissors,  the  slender  soft  spinal  cord  lying  in  its  tutx: 
will  come  into  view. 


CHAPTER  II. 

THE  MICROSCOPICAL  AND  CHEMICAL  COMPOSITION  OF 
THE  BODY. 

What  the  tissues  are  like.— Having  gained  some  idea 
of  how  the  larger  parts  of  the  body  are  arranged  we  may 
next  inquire  what  the  tissues,  its  smallest  .parts  which  are 
combined  to  make  the  larger,  are  like. 
The  simplest  tissues  are  known  as  cells;* 
they  are  so  small  that  a  separated  cell  can 
only  be  seen  with  the  help  of  a  microscope. 
In  a  fully  formed  cell  (Fig.  5)  we  find  three 
parts  :  (1)  a  cell  body  made  up  of  a  soft 
granular  substance  ;  (2)  a  smaller  and  less 
granular  cell  nucleus  imbedded  in  the  cell 
body  ;  and  (3)  a  tiny  dot,  the  nucleolus, 
lying  in  the  nucleus.  Cells  vary  much  in 
form  and  size,  though  all  are  very  small.  A 
good  many,  like  those  represented  at  b, 
float  in  our  blood,  and  are  more  or  less 
rounded.  In  other  places  cells  are  flattened  to  form  thin 
scales  as  those  in  Fig.  6,  which  represents  cells  scraped 

Of  what  are  the  larger  parts  of  the  body  made  up  ?  What  are 
the  simplest  tissues  ?  What  instrument  must  we  employ  in  order  to 
see  them  ?  Describe  the  structure  of  a  cell.  Describe  some  different 
forms  of  cells. 

*  So  called  from  an  old  belief  that  they  were  little  bags  or  chambers.  Most 
cells  are  really  solid  or  semisolid  throughout. 

[15] 


FiG.'5. — Forms 
of  cells  from  the 
body. 


16 


THE    HUMAN   BODY. 


from  the  inside  of  the  wall  of  the  abdomen.  Elsewhere 
we  find  cells  elongated,  as  c,  Fig.  5  ;  if  this  goes  on  to  any 
great  extent  we  get  a  long  slender  thread  which  is  called 
&Jiber;  but  very  often  fibers  are  made  by  a  number  of 
cells,  all  elongating  a  little  and  then 
joining  together  end  to  end.  Ex- 
amples of  fibers  are  shown  in  Figs.  35 
and  85.  Speaking  in  general  terms, 
we  may  say  that  the  whole  body  con- 
sists of  tiny  cells,  either  rounded  and 
thick,  flat  and  thin,  or  elongated  to 
form  fibers.  Just  as  a  wall  is  built 
of  distinct  bricks  or  stones,  so  an 
organ  is  made  up  of  a  number  of  cells. 
All  the  solid  parts  of  the  body  are 
either  cells  or  fibers  which  have  grown 
from  cells,  except  something  which  corresponds  pretty 
closely  to  the  mortar  which  lies  between  the  bricks  of  a 
wall  and  holds  them  together.  This  latter  material, 
known  in  the  body  as  intercellular  substance,  is  in  some 
places  abundant,  in  others  scanty  or  absent. 

Wherever  found,  the  intercellular  substance  is  made 
by  the  cells  which  lie  imbedded  in  it ;  they  pass  it  out 
from  their  surfaces  and  repair  it  when  necessary,  and  in 
this  respect  it  differs  very  essentially  from  the  mortar 
which  a  mason  lays  between  his  bricks. 

Summary. — Cells  are  thus  at  bottom  the  things  which 


FIG  6.— Flat  cells  from 
the  surface  of  the  lining 
membrane  of  the  abdo- 
men ;  a,  cell  body ;  b,  nu- 
cleus; c,  nucleoli. 


What  are  fibers  ?  How  are  they  made  ?  In  what  respect  may  an 
organ  be  compared  to  a  brick  wall  ?  What  corresponds  to  the  mortar 
of  the  wall  ?  What  makes  tlie  intercellular  substance?  How  ? 

State  briefly  the  relationship  of  its  cells  to  the  structure  and  work- 
ing of  the  body. 


MICROSCOPIC   COMPOSITION  OP  THE  BODY.      17 


make  up  the  body  and  do  its  work ;  their  forms  and  the 
way  they  are  arranged  together  determine  the  form  of  the 
organs  ;  the  things  which  the  kinds  of  cells  found-mi 
it  can  do,  determine  the  faculties  of  each  organ.  Some 
cells  can  make  a  great  deal  of  hard  intercellular  substance, 
and  are  employed  to  construct  the  skeleton  ;  others  can 
change  their  shape  and  are  used  to  form  the  organs  which 
move  the  body ;  others  can  elaborate  peculiar  solvent 
liquids  and  are  used  in  the  organs  of  digestion  ;  and  so  on 
through  all  the  parts.  Anatomy  in  the  long  run  is  a  study 
of  the  forms  which  cells  and  intercellular  substances  may 
assume  ;  and  physiology  a  study  of  what  the  cells  and  in- 
tercellular substances  of  the  body  can  do. 

The  physiological  division  of  labor. — In  a  tribe  of 
wandering  savages,  living  by  the  chase,  we  find  that  each 
man  has  no  special  occupation  of  his  own  ;  he  collects  his 
own  food,  provides  his  own  shelter,  defends  himself  from 
wild  beasts  and  his  fellow- men.  In  a  civilized  nation,  on 
the  contrary,  we  find  that  most  men  have  some  one  par- 
ticular business  :  farmers  raise  crops  and  cattle ;  cooks 
prepare  food  ;  tailors  make  clothes  ;  and  policemen  and 
soldiers  protect  the  properly  and  lives  of  the  rest  of  the 
community ;  in  other  words,  we  find  a  division  of  labor. 
Just  as  the  more  minute  the  division  of  employments  in  it 
is,  the  more  advanced  a  nation  is  in  civilization,  so  an 
animal  is  higher  or  lower  just  as  the  duties  necessary  for 
maintaining  its  existence  are  distributed  among  different 


What  determines  the  form  of  an  organ  ?  What  its  faculties  ? 
Give  examples  of  the  employment  of  cells  with  different  powers  to  do 
different  things.  What  is  Anatomy  really  ?  What  Physiology  ? 

Explain  what  is  meant  by  the  physiological  division  of  labor.  In 
what  class  of  nations  is  the  division  most  minute  ?  What  decides 
whether  an  animal  is  higher  or  lower  than  another  ? 


18  THE   HUMAN    BODY. 

tissues  and  organs.  In  the  lowest  animals  every  cell  is 
concerned  in  feeling,  and  moving,  and  catching  food,  and 
digesting,  and  breathing ;  in  higher  animals  different  cells 
are  set  apart  in  different  organs  for  the  execution  of  each 
of  these  separate  functions. 

Results  of  a  division  of  labor. — From  the  division  of 
employments  in  advanced  communities,  several  important 
consequences  result.  In  the  first  place,  when  every  one 
devotes  his  time  mainly  to  one  kind  of  work,  all  kinds  of 
work  are  better  done  :  the  man  who  always  makes  boots 
becomes  much  more  expert  than  the  man  who  is  engaged 
on  other  things  also  :  he  can  not  only  make  more  boots  in 
a  given  time,  but  he  can  make  better  boots ;  and  so  in 
other  cases.  In  the  second  place,  when  various  employ- 
ments are  distributed  among  different  persons  there  arises 
a  necessity  for  a  new  kind  of  industry  in  order  to  convey 
that  part  of  the  special  produce  of  any  given  individual 
which  may  be  in  excess  of  the  needs  of  himself  and  his 
family  to  others  .who  may  want  it,  and  to  bring  him  in 
return  such  of  their  excess  production  as  he  may  need. 
The  conveyance  of  food  from  the  country  to  cities,  and  of 
manufactures  to  agricultural  districts,  are  examples  of 
this  sort  of  labor  in  civilized  communities.  Finally,  there 
is  developed  a  necessity  for  arrangements  by  which,  at 
any  given  time,  the  activity  of  individuals  shall  be  regu- 
lated in  accordance  Avith  the  wants  of  the  whole  community 
or  of  the  world  at  large.  This  sort  of  regulation  is  still 

What  do  we  find  all  cells  doing  in  the  lowest  animals  ?  How  do 
higher  animals  differ  in  this  respect  ? 

How  does  a  division  of  labor  influence  the  quantity  of  work  done 
by  a  man  ?  How  the  quality  ?  Illustrate.  What  new  kinds  of 
employment  arise  when  a  division  of  labor  becomes  developed  in  a 
nation  ?  Illustrate. 


MICROSCOPIC   COMPOSITION   OF  THE  BODY.      19 

very  imperfectly  carried  oufc  even  in  the  most  advanced 
communities,  and  we  accordingly  hear  from  time  to  time 
of  the  over-production  of  this  or  that  article  ;  but  it  is  in 
part  effected  through  the  agency  of  capitalists  who  control 
the  activities  of  many  individuals  in  accordance  with  what 
they  think  to  be  the  quantity  of  various  articles  likely  to 
be  required  from  time  to  time. 

Exactly  similar  phenomena  result  from  the  division  of 
physiological  labor  in  the  human  body.  Each  tissue  and 
organ  doing  one  special  work  for  the  whole  body,  and  rely- 
ing on  the  others  for  their  aid  in  turn,  every  sort  of 
necessary  work  is  better  performed ;  the  tissue  or  organ, 
having  nothing  else  to  look  after,  is  constructed  with 
reference  only  to  its  own  particular  duty,  and  is  capable  of 
doing  it  extremely  well.  This,  however,  necessitates  a 
distributing  mechanism  by  which  the  excess  products,  if 
any,  of  the  various  organs,  shall  be  carried  to  others  which 
require  them  ;  and  a  regulating  mechanism  by  which  the 
activities  of  each  shall  be  controlled  in  accordance  with 
tTTeneeds  of  thn  whnlfi  body  at  the  time  being.  We  accord- 
mgly  find  a  set  of  organs,  the  heart  and  blood-vessels,  which 
carry  blood  from  place  to  place  all  over  the  body,  the 
blood  getting  in  its  course  something  from  and  giving 
something  to  each  organ  it  flows  through  ;  and  a  set  of 
nervous  organs  which  ramify  in  every  direction  and  regu- 
late the  activity  of  all  the  more  important  parts. 

Tlie  chemical  composition  of  the  body. — If  we  go  be- 
yond the  tissues  to  seek  the  ultimate  constituents  of  the 
body,  we  must  lay  aside  the  microscope,  and  call  in  chem- 

How  does  the  division  of  duties  in  it  affect  the  human  body  ? 
What  is  the  object  of  the  distributing  mechanism  ?  What  of  tha 
regulating  ?  What  are  the  distributing  organs  in  the  body  called  ? 
What  is  the  object  of  the  nerve  organs  ? 


20  THE    HUMAN    BODY. 

istry  to  our  aid,  to  discover  what  elements  and  compounds 
make  up  the  cells  and  intercellular  substance. 

Elements  found  in  the  body. — Of  the  elements,  about 
seventy  in  number,  known  to  chemistry,  only  sixteen  exist 
in  the  body.*  Very  few  of  these  exist  in  it  uncombined. 
Some  oxygen  is  dissolved  in  the  blood ;  and  it  is  also 
found  mixed  with  nitrogen  in  the  lungs. 

Chemical  compounds  existing  in  the  body. — These  are 
so  numerous  that  ib  would  be  a  long  task  to  enumerate 
them,  but  some  few  require  mention  :  they  may  be  divided 
into  organic  and  inorganic.  In  a  general  way  we  may  say 
that  the  organic  constituents  of  the  body,  if  all  water  were 
separated  from  them,  would  burn  if  put  in  a  fire  ;  and  the 
inorganic  components  could  not  be  made  to  burn. 

Inorganic  constituents  of  the  body. — Of  the  inorganic 
constituents  of  the  body,  water  and  common  salt  are  the 
most  important ;  they  are  found  in  all  the  organs  and 
liquids  of  the  body.  Phosphate  and  carbonate  of  lime  are 
found  in  large  proportions  in  the  bones  and  teeth  ;  and 
free  hydrochloric  acid  (spirits  of  salts  or  muriatic  acid) 
exists  in  the  gastric  juice,  which  dissolves  some  kinds  of 
food  in  the  stomach. 

Organic  constituents  of  the  body. — The  organic  con- 
stituents of  the  body  all  contain  carbon,  hydrogen,  and 


How  many  chemical  elements  exist  in  the  body  ?  Are  most  of 
them  free  or  combined  with  others  ?  Name  those  found  free. 

Into  what  main  groups  may  be  divided  the  chemical  compounds 
existing  in  the  body  ?  Name  some  of  the  chief  inorganic  compounds 
helping  to  build  the  body.  Where  are  they  found  in  it? 

What  do  all  organic  substances  in  the  body  contain? 


*  The  elements  found  in  the  body  in  health  are — carbon,  hydrogen,  nitrogen, 
oxygen,  sulphur,  phosphorus,  chlorine,  fluorine,  silicon,  sodium,  potassium,  lithium, 
e»lciiim,  magnesium',  iron,  and  manganese. 


CHEMICAL    COMPOSITION    OF    TEE    BODY.       $1 

oxygen ;  some  contain  nitrogen  also.    There  a'  3  three  chief 
kinds  of  them,  viz.  :  albumens^  fats,  and  carbohydrates. 

Albuminous  or  proteid  substances. — These  are  by  far 
the  most  characteristic  organic  compounds  existing  in  the  - 
body ;  /they  are  only  known  as  obtained  from  living  beings, 
having  never  yet  been  artificially  constructed  in  the  labor- 
atory-) a  good  example  is  found  in  the  white  of  an  egg, 
which  consists  chiefly  of  albumen  dissolved  in  water.  All 
the  tissues  of  the  body  which  have  any  marked  physiolog- 
ical property  contain  some  albuminous  substance,  only 
such  things  as  hairs,  nails,  and  teeth  being  devoid  of 
them.  All  albuminous  bodies  contain  nitrogen,  carbon, 
hydrogen,  and  oxygen  ;  most  of  them  sulphur  and  phos- 
phorus in  addition.  The  more  important  ones  found  in 
the  body  are,  (1)  Serum  albumen,  which  is  very  like  egg 
albumen,  and  is  found  dissolved  in  the  blood  ;  (2)  Fibrin, 
which  forms  in  blood  when  it  clots  ;  (3)  Myosin,  found  in 
the  muscles  and  "  setting"  or  coagulating  after  death,  when 
it  causes  the  death  stiffening  ;  (4)  Casein,  found  in  milk, 
and  forming  the  main  bulk  of  cheese. 

Fats  belong  to  the  organic  compounds  in  the  body 
which  contain  no  nitrogen  ;  they  consist  solely  of  carbon,  •, 
hydrogen,  and  oxygen.  The  chief  fats  in  the  body  are 
palmatin,  stearin,  and  olein;  by  proper  treatment  each 
can  be  split  up  into  glycerine  and  a  fatty  acid ;  palmitic, 
stearic,  or  oleic  acid  as  the  case  may  be. 

What  is  found  in  addition  in  some  of  them  ?  How  many  chief 
varieties  of  organic  compounds  are  there  in  the  body  ?  Name  them. 

Give  another  name  for  albuminous  substances.  Can  they  be  made 
artificially  ?  Give  an  example  of  an  albumen.  What  elements  do 
albumens  contain  ?  Name  the  more  important  albumens  of  the  body. 
Where  are  they  found  ? 

What  elements  do  fats  contain  ?  Name  the  chief  fats  of  tne  body. 
Into  what  may  they  be  decomposed  ? 


22  THE    HUMAN    BODY. 

The  carbohydrates  also  consist  entirely  of  carbon, 
hydrogen,  and  oxygen  ;  they  belong  to  the  same  class  of 
substances  as  starch  and  sugar.  The  most  important  car- 
bohydrate in  the  body  is  glycogen,  a  sort  of  starch  found 
stored  up  in  the  liver  and  muscles.  Glucose  or  grape 
sugar  also  exists  in  the  body ;  and  lactose  or  milk  sugar 
is  found  in  milk. 

What  elements  do  carbohydrates  contain  ?  Name  the  most  im- 
portant found  in  the  body  ?  Where  is  glycogcn  found  ?  Where 
milk  sugar  ? 


CHAPTER  III. 
THE    SKELETON. 

The  skeleton  *  of  the  human  body  is  composed  of 
three  materials  :  lone,  cartilage,  and  connective  tissue. 

The  bones  form  the  main  supporting  framework  of  the 
body,  and  determine  its  shape  ;  they  provide  levers  on 
which  the  muscles  moving  the  body  pull,  and  are  arranged 
so  as  to  surround  cavities  in  which  soft,  delicate  organs, 
as  brain,  spinal  cord,  and  heart,  may  lie  in  safety. 

Cartilage  finishes  off  many  bones  at  joints,  forming 
elastic  pads  with  smooth  surfaces  \,  it  is  also  used  instead 
of  bones  in  some  parts  of  the  skeleton  where  considerable 
flexibility  is  required.  Cartilage  affords  one  of  the  best 
tissues  of  the  body  for  the  examination  of  intercellular 
substance.  A  thin  slice  of  it  highly  magnified,  Fig.  7, 
shows  the  cartilage  cells,  a,  ~b,  scattered  through  an  almost 
structureless  material.  Very  young  cartilage  consists  of 

Of  what  is  the  skeleton  made  up  ?  What  functions  do  the  bones 
fulfill  ?  Where  is  cartilage  found  ?  What  are  its  purposes  ?  What 
is  seen  when  a  thin  slice  of  cartilage  is  highly  magnified  ?  Of  what 
does  young  cartilage  consist. 

*  There  are  two  kinds  of  skeleton  met  with  in  the  animal  kingdom  ;  the  external 
skeleton  or  exoskeleton,  and  the  internal  skeleton  or  endosketeton.  The  exoskeleton 
is  made  by  the  skin,  either  in  it  or  on  it ;  examples  are  found  in  the  shells  of  clams 
anu  lobsters :  the  scales  of  fishes  and  snakes  ;  the  tortoise-shell  of  turtles  ;  the 
feathers  of  bird5*;  the  hair  and  claws  of  beasts.  In  man  the  exoskeleton  is  only 
Slightly  developed,  hair,  uaiis  and  teeth  belong  to  it. 

[23] 


24  THE    HUMAN   BODY, 

the  cells  only,  but  these  lay  dx^wn  around  them  more  and 
intercellular  substance,  until  at  last  it  forms  the  main  bulk 


FIG.  7. — A  thiu  slice  of  cartilage  highly  magnified. 

of  the  cartilage,  and  gives  this  the  elasticity  and  flexibility 
for  which  it  is  used  in  the  body. 

Connective  Tissue  occurs  partly  in  the  form  of  stout 
cords — ligaments — which  bind  different  bones  together  ; 
or  which,  called  tendons,  attach  muscles  to  bones.  It 
also  supplements  the  coarser  bony  skeleton  by  a  finer 
one,  which  extends  as  a  fine  network  through  all  the  soft 
parts  of  the  body,  maKing  a  sort  of  microscopic  skeleton 

What  is  a  ligament  ?     A  tendon  ?     Of  what  are  ligaments  and        \ 
tendons  composed  ?     Where  else  do  Wi;  nnd  connective  tissue  ? 


SKELETON    OF   FOOT.  29 

the  knee-cap  or  patella,  q,  in  front  of  the  knee-joint ;  (4) 
of  twenty-six  foot  bones.  Of  the  foot  bones  seven,  the 
tarsal  bones,  n,  lie  below  the  ankle-joint  ;  five,  the  meta- 
tarsal  bones,  o,  succeed  these  in  the  front  half  of  the  sole 


Pas 


Fsa 


Fia.  10.— The  last  lumbar  vertebra  and  the  sacrum  seen  from  the  ventral  side. 
Fsa,  anterior  sacral  foramina. 

of  the  foot ;  and  fourteen  phalanges,  p,  are  found  in  the 
toes  ;  two  in  the  great  toe  and  three  in  each  of  the  others. 


Where  is  the  patella?  How  many  bones  are  there  in  each  foot? 
Into  what  groups  are  the  foot  bones  classified?  Where  are  the 
tarsal  bones?  How  many  ?  The  metatarsal  ?  How  many  ?  The 
phalanges  ?  How  many  ? 


30  THE    HUMAN   BODY. 

The  vertebral  column. — (Fig.  9.)  The  upper  portion 
of  the  spine  consists  of  twenty-four  separate  bones,  each 
called  a  vertebra;  these  are  piled  one  above  the  other,  and 
separated  by  elastic  pads  made  of  cartilage  and  connective 
tissue.  Seven  vertebrae  (cervical,  C  1-7)  are  found  in  the 
neck  ;  twelve  (dorsal,  D  1-12)  lie  at  the  back  of  the  chest 
and  carry  the  ribs ;  and  five  (lumbar,  L  1-5)  are  in  the 
loins. 

Below  the  separate  vertebrae  comes  the  sacrum,  (S  1), 
which  is  shown  as  seen  from  its  ventral  aspect  in  Fig.  10, 
along  with  the  lowest  lumbar  vertebra.  In  childhood  the 
sacrum  consists  of  five  distinct  vertebrae,  but  these  grow 
together  afterwards,  though  cross  ridges  remain  indicating 
the  original  lines  of  separation.  Succeeding  the  sacrum 
and  forming  the  lower  end  of  the  spine  is  the  coccyx  (Co, 
1-4,  Fig.  9),  a  single  bone  in  adults,  though  consisting  of 
four  pieces  in  children. 

The  structure  of  a  vertebra. — Those  vertebrae  which 
remain  permanently  separate  resemble  one  another  in 
general  form,  with  the  exception  of  the  uppermost  two. 
As  an  example  we  may  take  the  eleventh  from  the  skull, 
that  is  the  fourth  dorsal  vertebra  (Figs.  11  and  12). 

In  it  we  find  (1)  a  thick  bony  mass,  C,  rounded  on  the 
sides  and  flattened  above  and  below  where  it  is  turned 
toward  its  neighbors  ;  this  part  is  the  centrum  or  body  of 

Of  what  is  the  upper  portion  of  the  backbone  composed?  What 
.are  the  bones  forming  it  called?  What  lies  between  them?  How 
many  vertebrae  in  the  neck  ?  In  the  chest  region?  In  the  loins? 

Of  what  parts  is  the  lower  portion  of  the  vertebral  column  com- 
posed? How  many  vertebrae  form  the  sacrum?  At  what  period  of 
life  are  they  separate?  How  is  this  original  separation  indicated  on 
the  sacrum  of  adults?  How  many  vertebrae  are  united  to  form  the 
coccyx? 

What  vertebrae  differ  essentially  in  form  from  the  rest?  Describe 
a  typical  vertebra. 


A     VERTEBRA. 


31 


the  vertebra ;  the  series  of  vertebral  bodies  forms  the  bony 
partition  (<?,  e,  Fig.  1)  already  mentioned  as  existing  in  the 
trunk  between  the  neural  and  haemal  cavities.  (2)  An 
arch  attached  to  the  dorsal  side  of  the  centrum  ;  it  is  the 
neural  arch,  A,  and  with  the  centrum  incloses  the  neural 
ring  (Fv).  The  vertebrae  being  piled  one  above  the  other 
the  successive  neural  rings  form  the  neural  tube,  in  the 


7 

/ 


FIG.  11. 


FIG.  12. 


FIG.  11. — A  dorsal  vertebra  seen  from  behind,  i.«.,  the  end  turned  from  the 
head. 

FIG.  12.— Two  dorsal  vertebrae  viewed  from  the  left  side,  and  in  their  natural 
relative  positions.  6',  the  body  ;  A,  neural  arch  ;  Fv,  the  neural  ring ;  Ps,  spi- 
rious  process  ;  Pas,  anterior  articular  process  :  Pai,  posterior  articular  process  : 
Pt,  transverse  process  ;  Ft,  facet  for  articulation  with  the  tubercle  of  a  rib  ; 
Fes,  Fci,  articular  surfaces  on  the  centrum  for  articulation  with  a  rib. 

cavity  of  which  the  spinal  cord  lies.  (3)  Projecting  from 
the  body  and  arch  are  several  processes  ;  one  reaching  out 
from  the  dorsal  side  of  the  arch  is  the  spinous  process ; 
the  row  of  spinous  processes  which  may  be  felt  through 
the  skin  along  the  middle  of  the  back  has  given  the  name 
of  spinal  column  to  the  whole  backbone. 

AY  hat  constitutes  the  hard  partition  between  the  dorsal  and  ventral 
cavities  of  the  trunk?  How  is  the  neural  tube  formed?  Why  is 
the  spinal  column  so  named  ? 


THE    HUMAN    BODY 


Where  the  arch  joins  the  centrum  it  is  narrowed  to  a 
stalk  or  pedicle,  li,  Fig.  12.  When  the  vertebrae  are  placed 
together  in  their  natural  relative  positions,  apertures  (Fi), 
leading  into  the  neural  canal,  are  left  between  their  nar- 
rower portions ;  through  these  apertures  (called  the  inter- 
vertebral  foramina)  nerves  pass  out  from  the  spinal  cord. 

The  atlas  and  axis. — The  first  and  second  cervical  ver- 
tebras differ  considerably  from  the  others.  The  first, 
called  the  atlas  (Fig.  13),  carries  the  head  ;  it  has  a  very 


Aa   Fas 


D 


Fas 


Fai 


FIG.  13.  FIG.  14. 

FIG.  13.— The  atlas.  FIG.  14.— The  axis.  Aa,  body  of  atlas?.  Z>,  odontoid  pro- 
cess  of  axis ;  Fas.  facet  on  upper  side  of  atlas  with  which  the  skull  articulates ; 
and  in  Fig.  13,  anterior  articular  surface  of  axis ;  L,  transverse  ligament ;  Frt, 
vertebral  foramen. 

small  body  and  a  very  large  neural  ring.  A  ligament,  L, 
divides  the  ring  into  a  ventral  and  a  dorsal  portion  ;  the 
spinal  cord  passes  through  the  latter  and  a  bony  peg,  D, 
lies  in  the  former.  The  peg  is  the  odontoid  or  tooth-like, 
process.  This  reaches  up  from  the  second  cervical  or  axis 
vertebra  (Fig.  14)  and  forms  a  pivot  around  which  the  atlas, 

How  are  the  mtervertcbral  foramina  formed?  What  is  their  pur- 
pose? 

What  is  the  first  cervical  vertebra  called?  Describe  its  general 
form.  How  is  its  neural  ring  divided?  What  lies  in  each  division? 
What  is  the  second  cervical  vertebra  named?  What  is  the  odontoid 
process?  Around  what  pivot  does  the  head  rotate  when  the  face  is 
XUrnod  on  either  side? 


SPINAL    COLUMN.  33 

carrying    the    skull  with  it,    rotates  when    the  head   is 
turned  from  side  to  side. 

On  the  {interior  (upper)  surface  of  the  atlas  are  a  pair 
of  shallow  hollows,  Fas ;  into  these  fit  a  pair  of  knobs, 
found  towards  the  back  of  the  under  surface  of  the  skull 
(Fig.  20),  vvhich  glide  in  the  hollows  during  nodding 
movements  of  the  head. 

Uses  of  the  mode  of  structure  of  the  spinal  column.— 
When  the  backbone  is  viewed  from  one  side  (Fig.  9)  it  is 
seen  to  present  four  curvatures  ;  one  in  the  neck,  convex 
ventrally,  is  followed  by  a  curve  in  the  opposite  direction 
in  the  dorsal  region  ;  in  the  loins  the  curvature  is  again 
convex  ventrally,  and  opposite  the  sacrum  and  coccyx  the 
reverse  is  the  case.  These  curves  add  greatly  to  the 
springiness  of  the  spine,  and  prevent  the  transmission  of 
sudden  jars  along  it.*  The  compressible  elastic  pads  placed 
between  the  centra  of  the  vertebrae  promote  the  same  end ; 
the  skull,  containing  the  soft  brain  (which  would  be 
readily  injured  by  mechanical  violence)  and  the  spinal 
cord,  contained  in  the  backbone  itself,  are  thus  protected 
from  jarring  in  running,  jumping,  &c. 

The  compressible  pads  between  the  bodies  of  the  verte- 
bras allow  of  a  certain  range  of  movement  between   each 
pair,  so  that  the  column  as  a  whole   may  be  bent  to  a  con- 
How  is  the  skull  articulated  to  the  backbone? 
How  many  curvatures  are  there  in  the  backbone?     What  is  their 
direction? 

What  results  from  the  curvatures  of  the  spinal  column?  What  is 
the  object  of  the  pads  between  the  vertebrae? 


*  Take  a  straight  but  tolerably  flexible  and  elastic  bar,  as  a  lath,  or,  better  still,  a 
thin  steel  rod.  Hold  it  vertical,  with  one  end  resting  on  the  floor,  and  give  a  smart 
blow  on  the  upper  end  ;  the  jar  will  be  sudden  and  violent.  Now  bend  the  rod  and 
hit  it  again  ;  the  jar  will  be  much  less,  as  the  curved  rod  yields  somewhat  to  the 
blow  on  its  top. 


34  THE    HUMAN   BODY. 

siderable  extent  in  any  direction.  On  the  other  hand, 
these  pads  so  limit  the  movement  that  no  sharp  bend  can 
occur  at  any  one  point,  such  as  might  tear  or  bruise  the 
spinal  cord  lying  in  the  neural  canal. 

The  sacral  vertebrae  grow  together  firmly  to  give  a 
solid  support  to  the  pelvic  arch,  which  transmits  the 
weight  of  all  the  rest  of  the  body  to  the  lower  limbs  when 
we  stand. 

Summary. — The  back-bone  is  rigid  enough  to  sup- 
port all  the  rest  of  the  body  ;  flexible  enough  to  bend 
considerably  in  any  desired  direction,  yet  not  sharply  at 
any  one  point ;  and  elastic  enough  to  destroy  or  greatly 
diminish  any  sudden  jar  or  jerk  which  it  may  receive.  It 
is  one  of  the  most  beautiful  pieces  of  mechanism  in  the 
body. 

The  ribs  are  twelve  in  number  on  each  side   (Fig.  15). 
They  are  slender  curved  bones  embracing  the  sides  of  the 
chest,  and   attached  at  one  end  to   the   dorsal   vertebrae. 
Ventrally  each  rib  ends  in  a  costal   cartilage;  the   carti- 
lages of  the  seven  upper  pairs  are  directly  articulated  to 
the  sides  of  the  breast-bone.     The    eighth,    ninth,    and 
/ij    tenth  cartilages  join  those  of  the  ribs  above   them  ;   the 
eleventh  and  twelfth  are  not  attached  to  the  rest  of  the 
skeleton  at  their  ventral  ends,  and  are  known  as  the  free 
v     or  floating  ribs. 

Flow  is  it  that  we  can  bend  the  backbone?  How  is  the  extent  of 
bending  at  any  one  point  limited?  Why? 

Why  do  the  sacral  vertebrae  grow  together? 

State  briefly  the  mechanical  properties  of  the  vertebral  column. 

How  many  ribs  are  there  ?  What  is  their  shape  ?  To  what  are 
their  dorsal  ends  attached?  How  does  each  rib  end  ventrally?  To 
what  are  the  costal  cartilages  of  the  first  seven  ribs  attached?  To 
what  the  next  three  costal  cartilages?  Which  are  the  floating  ribs? 
Why  so  called? 


TEE   SKULL. 


35 


vertebra, 


The  skull  (Fig.  16)  is  composed  of  twenty-eight  bones  : 
these,  forming  the  cranium,  are  so  arranged  as 
How  many  bones  in  the  skull? 


36 


THE    HUMAN   BODY. 


to  surround  the  brain  and  protect  the  ears  ;  six  lie  inside 
the  ears ;   and  the  remaining  fourteen  support  the  face, 
Tsp 


PIG.  16.— A  side  view  of  the  skull.  <9,  occipital  bone ;  T,  temporal  •  TV,  parie- 
tal ;  F,  frontal ;  S.  sphenoid  ;  Z,  malar  ;  MX,  maxilla  ;  2V,  nasal ;  Et  ethmoid  ;  L, 
lachrymal ;  Md.  inferior  maxilla. 

surround  the  mouth  and  nose,  and  (with  the  aid  of  some 
of  the  cranial  bones)  form  the  eye-sockets. 

How  many  in  the  cranium?  What  purposes  do  the  cranial  bones 
fulfill?  How  many  lie  inside  the  ears?  How  many  bones  in  the 
face?  What  parts  do  the  face  bones  support  and  protect? 


CRANIUM.  37 

The  cranium  is  a  box  with  a  thick  floor  (Fig.  1),  con- 
tinuing forwards  the  partition  which  in  the  trunk  separates 
the  neural  from  the  haemal  cavity.  On  its  under  side 
(Fig.  20)  are  many  small  apertures  through  which  nerves 
and  blood-vessels  pass  in  or  out,  and  one  larger  one,  the 
foramen  magnum,  through  which  the  spinal  cord  passes 
in  to  join  the  brain. 

The  cranial  bones  (Fig.  16)  are  the  following  :  1.  The 
occipital  lone,  0,  unpaired,  and  having  in  it  the  fora- 
men magnum.  It  lies  at  the  back  of  the  skull.  2.  The 
frontal  hone,  F,  also  unpaired,  lies  in  the  forehead.  3. 
The  parietal  bones,  Pr,  two  in  number,  meet  one  another 
above  the  middle  of  the  crown  of  the  head,  and  form  a 
great  part  of  the  roof  and  sides  of  the  skull.  4.  The  tem- 
poral bones,  T,  ^ne  on  each  side,  opposite  the  temples ;  on 
the  exterior  of  each  temporal  bone  is  a  large  aperture 
leading  into  the  ear  cavity,  which  is  contained  in  this 
bone.  5.  The  sphenoid  hone,  unpaired,  and  lying  in  the 
middle  of  the  base  of  the  skull,  but  sending  out  a  wing,  S, 
which  reaches  some  way  up  each  side,  just  in  front  of  the 
temporal.  6.  Tlie  ethmoid  hone,  E,  forms  the  partition  be- 
tween the  brain  and  nose  chambers,  and  part  of  that  be- 
tween the  nose  and  the  eye  socket. 

The  facial  skeleton. — The  majority  of  the  face  bones 
are  in  pairs,  but  two  are  single ;  one  of  these  is  the  lower 
jaw  hone  or  mandible,  Md,  Fig.  16 ;  the  other  is  the  vomer, 

With  what  is  the  floor  of  the  cranium  continuous?  Where  does 
the  cranium  present  holes  through  it?  What  are  most  of  these  aper- 
tures for?  What  is  the  largest  aperture  called?  What  enters  the 
brain  case  through  it? 

Name  the  cranial  bones.  State  where  each  lies.  Through  which 
does  the  foramen  magnum  pass?  Which  contains  the  ear  chamber? 
Which  of  them  are  unpaired? 


38  THE    HUMAN   BODY. 

which,  forms  part  of  the  partition  between  the  two 
nostrils. 

The  paired  face  bones  are  :  1.  The  maxiUcB  or  upper 
jaw-bones,  MX,  which  carry  the  upper  teeth  and  form 
most  of  the  hard  palate  separating  the  mouth  from  the 
nose.  2.  The  palate  bones,  completing  the  bony  palate,  and 
behind  which  the  nostril  chambers  communicate  by  the 
posterior  nares  (Fig.  20)  with  the  throat  cavity,  so  that  air 
can  pass  in  or  out  through  them  in  breathing.  3.  The 
malar  or  cheek-bones,  Z.  4.  TJte  nasal  bones,  N,  roofing  in 
the  upper  part  of  the  nose.  5.  The  lachrymal  or  tear- 
bones,  L,  small  and  thin,  lying  between  the  eye-socket  and 
the  nose.  6.  The  inferior  turbinate  or  spongy  bones,  which 
lie  inside  the  nose,  one  on  the  outer  side  of  each  nostril 
chamber. 

The  cranial  sutures. — All  the  bones  of  the  skull,  except 
the  lower  jawbone,  are  immovably  joined  together.  In  the 
case  of  most  of  the  cranial  bones  this  occurs  by  a  dove- 
tailing, like  that  used  by  cabinet-makers.  Each  bone  has 
its  edges  notched,  and  the  notches  fit  accurately  into  hol- 
lows on  the  bone  it  articulates  with  ;  this  kind  of  articula- 
tion is  called  a  suture  ;  it  is  well  seen  in  Fig.  16,  between 
the  parietal  bone  and  those  in  front  of,  behind,  and 
below  it. 

Comparison  of  the  upper  and  lower  limbs  and  their 
supporting  arches.  The  bones  of  these  have  already 


Name  the  unpaired  face  bones. 

Where  does  each  lie?  Name  the  paired  face  bones.  State  the 
position  of  each  in  the  skull.  What  bone  carries  the  lower  teeth? 
Which  the  upper?  What  bones  form  the  hard  palate?  By  what 
openings  do  the  nose  chambers  communicate  with  the  throat?  Behind 
what  bone  do  these  openings  lie? 

What  cranial  bone  is  movable?  How  are  most  of  the  cranial 
bones  joined  together?  Describe  a  suture? 


SKELETONS    OF   LIMBS. 


FIG.  17.— The  skeleton  of  the  arm  and  leer.  17,  the  hnmerus  ;  Cd,  its  articu». . 
head  which  fits  into  the  glenoid  fossa  of  the  scapula  ;  U,  the  ulna  ;  72,  the  ra- 
dius ;  0,  the  olecranon ;  Fe,  the  femnr ;  f,  the  patella ;  M,  the  fibula ;  T 
the  tibia. 

been  enumerated,  but  certain  resemblances  and  diffei- 
ences  between  the  skeletons  of  the  two  limbs  (Fig.  17) 
are  worth  noting.  In  general  plan  it  is  clear  that  they 


40  TUE   HUMAN   BODY. 

correspond  pretty  closely  to  one  another;  the  pectoral 
arch  answers  to  the  pelvic  ;  the  humerus  to  the  femur ; 
the  radius  and  ulna  are  represented  by  the  tibia  and 
fibula  ;  five  metacarpal  bones  correspond  to  fiye  metu- 
tarsal,  and  fourteen  phalanges  in  the  digits  of  the  hand  to 
fourteen  in  the  digits  of  the  foot ;  elbow  and  knee-joints, 
and  wrist  and  ankle  are  comparable.  There  is,  however, 
in  the  arm  no  separate  bone  at  the  elbow  answering  to  the 
patella  at  the  knee  ;  but  the  ulna  bears  above  a  bony 
process,  0,  which  is  in  early  life  a  separate  bone  and 
represents  the  patella.  There  are  in  the  adult  carpus 
eight  bones,  in  the  tarsus  but  seven ;  here  again  we  find, 
however,  that  originally  the  astragalus,  Ta  (Fig.  19),  of 
the  tarsus  consists  of  two  bones.  The  elbow-joint  bends 
ventrally^ud  the  knee-joint  dorsally. 

When  we  compare  the  limbs  as  a  whole  greater  differ- 
ences come  to  light,  differences  which  are  related  to  their 
different  uses.  The  arms,  serving  as  prehensile  organs, 
have  all  their  parts  as  movable  as  is  consistent  with  the 
requisite  strength  ;  the  lower  limbs,  having  to  carry  all  the 
weight  of  the  body,  have  their  parts  more  firmly  knit 
together.  Accordingly  we  find  the  shoulder  girdle,  C,  8 

Do  the  upper  and  lower  limbs  correspond  in  general  plan  of  struc- 
ture ?  What  in  the  lower  limb  answers  to  the  pectoral  girdle  ? 
What  to  tho  humerus  ?  What  bones  to  those  of  the  forearm  ?  What 
to  the  metacarpal  ?  Do  the  phalanges  of  the  hand  and  foot  agree  in 
number  ?  What  joints  in  the  leg  answer  to  elbow  and  wrist  ? 

What  bone  in  the  leg  is  not  represented  by  a  separate  bone  in  the 
arm  of  adults?  What  in  the  arm  corresponds  to  this  leg  bone?  Is  it 
ever  a  separate  bone?  Which  has  more  bones,  hand  or  foot?  How 
many  bones  are  there  in  the  tarsus  in  infancy?  How  many  after 
wards  unite  to  form  one?  What  is  the  bone  formed  by  this  union 
named?  How  do  elbow  and  knee  joints  differ  as  to  the  direction  in 
which  they  bend? 

Why  are  the  arms  made  as  movable  as  possible?  Why  ar«  tia 
lower  limb  bones  more  firmly  knit? 


SHOULDER    AND    PELVIS. 


41 


Pig.  18,  only  directly  attached  to  the  axial  skeleton  by  the 
ventral  ends  of  the  collar  bones,  and  free  to  make  consid- 


Fia.  18.— The  skeleton  of  the  trunk  and  the  limb  arches  seen  from  the  front. 
C.  clavicle  ;  S,  scapula  ;  Oc,  innominate  bone  attached  to  the  side  of  the  saorum 
dorsally  and  meeting  its  fellow  at  the  pubic  symphysis  in  the  ventral  median  line. 

erable  movements,  as  in  "shrugging  the  shoulders."  The 
pelvic  girdle,  Oc,  on  the  contrary,  is  firmly  and  immova- 
bly attached  to  the  sides  of  the  sacrum. 

How  is  the  shoulder  girdle  united  to  the  axial  skeleton? 
Can  it  move?    Give  an  instance?     How  is  the  pelvic  attached?    Is 
it  movable? 


42  THE    HUMAN   BODY. 

The  socket  on  the  outer  end  of  the  shoulder-blade,  with 
which  the  humerus  forms  the  shoulder-joint,  is  very  shal- 
low, and  allows  of  much  freer  movement  than  is  permitted 
by  the  deeper  socket  of  the  pelvis,  into  which  the  top  of 
the  thigh  bone  fits. 

If  we  hold  one  humerus  tightly  and  do  not  allow  it  to 
rotate,  we  can  still  move  the  forearm  bones  so  as  to  turn 
the  palm  of  the  hand  up  or  down ;  no  such  movement  is 
possible  between  tibia  and  fibula. 


Cl      C?     XT  SfH 


FIG.  19.— The  bones  of  the  foot.    Ca,  calcaneum,  or  heel  bone;  Ta,  articular 
Btuface  for  tibia  on  the  astragalus  ;  Cb,  the  cuboid  bone. 


In  the  foot  the  bones  are  much  less  movable  than  in 
the  hand,  and  are  so  arranged  as  to  make  a  springy  arch 
(Fig.  19)  which  bears  behind  on  the  heel  bone,  Ca,  and  in 
front  on  the  far  ends,  Os,  of  the  metatarsal  bones ;  over 
the  crown  of  the  arch  at  Ta  is  the  surface  with  which  the 
leg-bones  articulate,  and  on  which  the  weight  of  the  body 
bears  when  we  stand. 


Which  is  deeper,  the  socket  on  shoulder-blade  for  humerus,  or  on 
pelvic  girdle  for  femur? 

Can  the  foot  be  turned  round  so  as  to  bring  its  sole  upwards? 
Can  the  hand  so  as  to  bring  the  palm  up? 

Are  the  hand  or  the  foot  bones  more  movable?  How  are  the  foot 
bones  arrans^d?  On  what  points  does  the  arch  of  the  foot  bear?  On 
what  part  of  the  arch  is  the  weight  of  the  body  borne? 


PECULIARITIES   OF  HUMAN  SKELETON.         43 

The  toes  are  far  less  mobile  than  the  fingers,  the 
difference  between  great  toe  and  thumb  being  especially 
marked.  The  thumb  can  be  made  to  meet  each  of  the 
finger-tips,  and  so  the  hand  can  seize  and  manipulate  very 
small  objects,  while  this  power  of  opposing  the  great  toe 
to  the  others  is  nearly  absent  in  the  foot  of  civilized  man. 
In  infants,  and  in  savages  who  have  never  worn  boots,  the 
great  toe  is  often  much  more  movable,  though  it  never 
acts  so  completely  like  a  thumb  as  it  does  in  most  apes, 
whose  feet  are  used  for  prehension  nearly  as  much  as  their 
hands.  Our  own  toes  can  by  practice  be  made  much  more 
movable  than  they  usually  are ;  persons  born  without 
hands  have  learned  to  write  and  paint  with  the  toes. 

Peculiarities  of  the  human  skeleton. — -There  are  some 
interesting  points  in  the  structure  of  the  human  skeleton, 
connected  with  our  power  of  maintaining  the  erect  posture, 
and  of  progressing  on  the  feet  so  that  the  hands  are  left 
free  for  grasping.  In  no  other  vertebrate  is  the  division 
of  labor  between  the  anterior  and  posterior  limbs  carried 
so  far ;  the  highest  apes  often  use  the  hand  in  locomotion 
and  the  foot  for  prehension.  As  characteristic  of  man's 
skeleton  we  may  note  : 

1.  The  skull  is  nearly  balanced*  on  the  top  of  the  verte- 
bral column  (Fig.  20)  so  that  but  little  effort  is  needed  to 

Are  toes  or  fingers  more  mobile?  How  does  the  thumb  differ  in 
this  respect  from  the  great  toe?  What  reason  have  we  to  think  that 
tl  e  shoe  has  produced  this  effect  ?  in  what  animals  is  the  great  toe 
more  movable  ?  What  power  have  their  feet  in  consequence  ?  Can 
we  make  our  toes  more  movable  by  practice  ?  Illustrate. 

With  what  facts  are  the  more  marked  peculiarities  of  the  human 
skeleton  connected?  In  what  living  creature  is  the  division  of 
labor  between  arms  ,nd  legs  carried  farthest? 

Does  the  skull  of  man  nearly  balance  on  its  support? 

*The  balance  is,  however,  not  quite  complete.  When  any  one  goes  to  sleep  in 
an  ill-ventilated  lecture  room  he  is  usually  awakened  by  a  sharp  jerk  downwards  of 


44 


THE    HUMAN   BODY. 


keep  the  head  erect.  In  four-footed  beasts  the  skull,  being 
carried  on  the  front  end  of  a  horizontal  backbone,  needs 
special  ligaments  and  considera- 
ble muscular  effort  to  support  it  : 
in  apes  the  skull  does  not  nearly 
balance  on  the  top  of  the  spine  ; 
its  face  is  much  heavier  than  its 
back  part,  while  in  men  the  face 
bones  are  relatively  smaller  and 
the  cranium  larger.  To  keep  the 
head  erect  and  look  things 
straight  in  the  face  "  like  a  man  " 
is  far  more  fatiguing  to  monkeys, 
and  they  cannot  maintain  that 
position  long. 

2.  The  human  spinal  column, 
when   viewed   from  the   front,  is 

of  the  mouth  and  surrounded  by 

the  upper  set  of  teeth.    Above   seen  to  widen  gradually  from  the 

this  are  the  paired  openings  of 
the  posterior  nares.  and  a  short 
way  above  the  middle  of  the  fig- 
ure is  the  large  median  foramen 
magnum,  with  the  bony  convex- 


FIG.  20.— The  base  of  the  skull. 
The  lower  jaw  has  been  removed. 
At  the  lower  part  of  the  figure  is 
the  hard  palate  forming  the  roof 


neck   to  the  sacrum,    and  so  to 
be    well    fitted    to    sustain    the 
weight  of  the  head,  upper  limbs, 
of^ht^kuirbehtd  £S  &c.,  carried  by  it.  Its  curvatures, 


which  are  peculiarly  human,  add 

in  an  ape  the  portion  in  front  of  ,n  •,  •  j     i      ,•    •> 

the  occipital  condyies  would  be    greatly  to  its  spring  and  elasticity; 

much   larger  than   that  behind  .    -,  ,       •    •  -\          -\     ji 

them.  were  it  a  straight  rigid  rod    the 

brain,  concealed  in  the  skull  at  its  top,  would  be  jarred  at 
every  step. 

How  do  four-footed  beasts  differ  in  this  respect?  Do  apes'  skulls 
balance  as  well  as  man's?  Why  not?  What  is  the  result  of  this 
want  of  balance? 

What  is  observed  when  the  human  spinal  column  is  viewed  from 
the  front?  What  is  gained  by  its  gradual  widening  from  above 
down?  What  feature  in  our  spines  is  peculiarly  human?  What 
benefit  results  from  it? 

his  chin.    The  muscles  concerned  In  holding  the  head  erect  having  relaxed  their 
vigilance  the  greater  weight  of  the  front  half  of  ihe  skull  exerts  its  effect. 


PECULIARITIES    OF    SKELETON.  45 

3.  The  pelvis,  to  the  sides  of  which  the  lower  limbs  are 
attached,  is  proportionately  very  broad  in  man,  so  that  the 
balance  of  the  trunk  on  the  legs  is  not  easily  upset  when 
the  body  is  bent  towards  one  side. 

4.  The  lower  limbs  are  proportionately  very  long  in 
man.     This  makes  progression  on  them  more  rapid   by 
allowing  a  longer  stride,  and  also  makes  it  difficult  to  go 
on   "all   fours"   except  by  creeping  on   the   hands   and 
knees.     The  arms  of  some  apes  are  as  long,  and  of  others 
longer,  than  their  legs. 

5.  The  arched   instep  and    broad  sole  of   the  human 
foot  are  very  characteristic.     Most  beasts,  as  horses,  walk 
on  the  tips  of  their  toes,  the  hoof  being  really  a  very  big 
nail ;  others,  as  bears,  place  the  heel  also  on  the  ground, 
but    have    a    much    less    developed    tarsal    arch     than 
man.     The  vaulted  human  tarsus,  made  up  of  a' number 
of  small  bones,  each  of  which  can  glide  a  little  over  its 
neighbors,  but  none  of  which  can  move  much,  is  admira- 
bly calculated   to   break  any  jar  which  might  be  trans- 
mitted to  the  spinal  column  by  the  contact  of  the  sole 
with  the  ground  at  each  step.*     A  well  arched  instep  is 

What  feature  characterizes  the  human  pelvis?  What  benefit 
results  from  it?  Which  limbs  are  longest  in  man?  What  ends  are 
gained  by  the  considerable  length  of  the  legs?  Why  do  infants  crawl 
on  the  hands  and  knees  instead  of  the  hands  and  feet?  Which  limbs 
are  longest  in  apes? 

What  structural  points  in  the  foot  are  especially  human?  What 
part  of  the  foot  do  horses  put  on  the  ground?  Name  an  animal 
which  puts  the  heel  also  on  the  ground  when  it  walks.  How  does 
the  bear's  tarsal  arch  differ  from  man's? 

"What  benefit  results  from  the  form  and  structure  of  the  human 
tarsus?  How?  Why  is  a  well-arched  instep  beautiful? 


*  A  carriage  spring  consists  of  two  curved  elastic  steel  bars  fastened  together  at 
their  ends,  and  with  their  concave  sides  turned  towards  one  another.  The  axle  of 
the  wheel  is  attached  to  the  middle  of  the  lower  bar,  and  the  weight  of  the  carriage 


46  THE    HUMAN   BODY. 

therefore  rightly  considered  a  beauty;  it  makes  the  gait 
easier  and  more  graceful. 

bears  on  the  middle  of  the  upper.  When  the  wheel  jolts  over  a  stone  the  jerk  is 
transmitted  to  the  elastic  arches,  which  each  flatten  a  little,  and  so  instead  of  a  sud- 
den jerk  a  gentle  sway  is  transmitted  to  the  carriage.  The  tarsal  arch  of  the  hu- 
man foot  acts  like  the  upper  half  of  a  carriage  spring. 


IV. 

THE    STRUCTURE,    COMPOSITION    AND    HYGIENE    OF 

BONES. 

The  gross  structure  of  bones. — Although  the  bones 
differ  very  much  in  shape  all  are  alike  in  microscopic 
structure  and  in  chemical  coir  _;tion.  When  alive  they 
have  a  bluish-white  color,  with  a  pinkish  hue  when  blood 
is  flowing  through  them ;  they  possess  considerable  flexi- 
bility and  elasticity,  which  may  be  best  observed  in  a  long 
slender  bone,  as  a  rib.* 

To  get  a  general  idea  of  the  structure  of  a  bone  we 
may  select  the  humerus  (Fig.  21).  When  fresh  this  is 
closely  invested  on  its  outside  by  a  tough  membrane,  the 
periosteum,  composed  of  .connective  tissue  and  containing 
many  blood-vessels.  On  its  under  side  new  bony  tissue  is  de- 
posited as  long  as  the  bone  is  growing  thicker,  and  through- 
out life  it  is  concerned  in  the  nourishment  of  the  bone, 

How  do  bones  differ  from  one  another?  In  what  respects  do  all 
bones  agree?  What  is  the  color  of  a  living  bone?  Name  some  mechan- 
ical properties  of  bone.  In  what  bones  may  such  properties  be  most 
readily  seen? 

What  covers  a  bone  on  the  exterior?  What  is  it  composed  of? 
Does  it  contain  bloodvessels? 


*  The  rib  of  a  sheep  or  a  rabbit  when  thoroughly  boiled  can  be  readily  scraped 
clean  and  preserved,  and  serves  admirably  to  show  the  flexibility  and  elasticity  of 
bone. 

[47J 


48 


THE   HUMAN   BODY. 


Cp 


FIG.  21.-The 
from  the  front, 
text. 


r  description  Tee 


which  dies  if  it  be  stripped 
off.*  The  periosteum  covers 
the  humerus  except  on  its 
ends  (Cp,  Tr,  Cpl)  at  the 
shoulder  and  elbow- joints  ; 
there  the  bone  is  covered  by 
a  thin  layer  of  gristle  or  car- 
tilage. Very  early  in  life  the 
whole  humerus  consists  of 
cartilage  ;  this  is  afterwards 
absorbed  and  replaced  by 
bone,  leaving  only  a  thin 
layer  of  articular  cartilage 
on  each  end. 

The  bone  itself  consists 
of  a  central  nearly  cylindrical 
portion  or  shaft  (extending 
between  the  dotted  lines  X 
and  Z)  and  two  articular  ex- 
tremities. These  extremities 
are  enlarged  to  give  a  wider 

What  are  the  functions  of  the 
periosteum?  Where  is  the  perios- 
teum absent?  Of  what  does  the 
humerus  consist  in  very  early  in 
life?  What  happens  to  most  of  its 
cartilage  afterwards  ?  Where  is 
some  cartilage  left? 

What  are  the  main  divisions  of 
the  humerus?  What  is  the  general 
form  of  its  shaft  ?  Why  are  its  ar- 
ticular extremities  large? 

*  Cases  have  been  recorded  in  which  a 
considerable  portion  of  a  bone  or  even  the 
whole  bone  has  been  removed  during  life, 
and  the  periosteum  Oeft  but  slightly  in- 
jured) has  formed  a  new  bone  in  place  of 
the  old. 


STRUCTURE  OF  BONES. 


49 


bearing  surface  in  the  joints,  and  also  to  provide  space 
on  which  to  attach  the  muscles  which  move  the  bone  ;  the 
various   knobs  on  the  extremities,   and 
the  rough  patches  on  the  shaft,  all  mark 
areas  where  muscles  were  fixed. 

Internal  structure. — If  the  humerus 
were  divided  lengthwise  we  would  find 
that  its  shaft  was  hollow  ;  the  space  is 
known  as  the  medullary  cavity,  and  in 
life  is  filled  with  soft  fatty  marrow.  Fig. 
22  represents  such  a  longitudinal  section. 
We  see  in  it  that  the  marrow  cavity  ends 
near  the  articular  extremities ;  and  that 
in  these  the  hone  has  a  loose,  spongy  text- 
ure, except  a  thin  dense  layer  on  the  sur- 
face. In  the  shaft  the  compact  outer 
layer  is  much  the  thicker,  the  spongy 
portion  only  forming  a  thin  stratum  next 
the  medullary  cavity.*  To  the  unas- 
sisted eye  the  spongy  bone  appears  made 
up  of  a  trellis- work  of  thin  bony  plates 
which  intersect  in  all  directions  and  sur- 
round cavities  about  the  size  of  the 

What  do  the  knobs  and  rough  patches  on  the 
bone  indicate? 

What  should  we  find  on  dividing  the  hu- 
merus lengthwise?  What  is  its  shaft  cavity 
called?  What  does  it  contain?  Where  does 
the  marrow  cavity  end?  What  is  the  texture  of 

the  articular  extremities  of   the   bone?     How     FIG.  22.—  The  humerus 
does  the  shaft  differ  in  structure  from  the  ex-  cut  open,     a,  marrow 
tremities  of  the  femur?    What  does  the  spongy  «Jg5 
bone  look  like?  lae. 


*  These  facts  may  readily  be  demonstrated  by  sawing  in  two  lengthwise  the 
bones  out  of  a  leg  of  mutton. 


50  THE   HUMAN   BOD7 

head  of  a  small  pin.  In  these  spaces  there  is  found  dur- 
ing life  a  substance  known  as  the  red  marrow,  which  is 
quite  different  from  the  yellow  fatty  marrow  of  the  medul- 
lary cavity.* 

Why  bones  are  hollow. — If  the  bones  were  solid  they 
would  be  extremely  heavy  and  unnecessarily  strong  for 
the  common  purposes  of  life,  unless  only  the  same  amount 
of  material  were  used  in  their  construction,  and  then  they 
would  be  either  loose  in  texture  and  easily  broken,  or, 
if  dense,  they  would  be  thin  rods  and  not  give  sufficient 
surface  for  the  attachment  of  muscles.  It  is  a  well-known 
principle  in  practical  mechanics  that  the  same  amount  of 
material  will  bear  a  greater. strain  if  in  the  form  of  a  tube 
than  in  that  of  a  solid  rod  of  the  same  length  ;  hence  iron 
pillars  are  cast  hollow  ;  to  fill  them  up  solidly  would  make 
them  enormously  heavier  without  anything  like  a  propor- 
tionate increase  in  strength.  Take  a  glass  tube  one  foot 
long  and  a  piece  of  glass  rod  of  the  same  length  and 
weight ;  support  each  at  its  ends  and  hang  weights  on  the 
middle  until  it  breaks  ;  the  tube  will  be  found  to  bear  a 
very  much  greater  strain  before  yielding.  We  see  an  ap- 
plication of  this  same  method  of  utilizing  a  given  amount 
of  material  to  the  best  advantage  for  support,  in  the  hol- 
low stalks  of  grass,  wheat  and  barley; 

Varieties  of  structure  found  in  different  bones. — Bones 
which,  like  the  humerus  and  femur,  present  a  shaft  and 


What  lies  in  the  cavities  of  the  spongy  bone  ° 

Why  are  most  bones  hollow?  Which  will  bear  most  weight,  a 
tube  or  a  solid  rod  of  the  same  material,  weight,  and  length?  Give 
illustrations.  Why  are  grass  stalks  hollow? 

*Many  of  the  bones  of  birds  are  thin  walled  tubes  of  dense  bone  :  the  centraj 
cavity  contains  air  and  no  marrow,  and  communicatec  by  tubes  with  the  luiigs. 
Examine  the  humerus  of  a  pigeon  or  a  rooster. 


HISTOLOGY    OP   BONM.  51 

articular  extremities,  are  called  long  bones ;  other  examples 
are  tibia  and  fibula,  radius  and  ulna,  metacarpal  and  meta- 
tarsal  bones,  and  the  phalanges  of  fingers  and  toes.  Tab- 
ular bones  form  thin  plates,  like  those  of  the  roof  of  the 
skull,  and  the  shoulder-blades.  Short  bones  are  rounded 
or  angular,  and  not  much  longer  in  one  diameter  than 
another  ;  as  the  carpal  andtarsal  (Fig.  19)  bones.  Irregu- 
lar bones  include  all  which  do  not  fit  well  into  any  of  the 
above  classes  ;  they  usually  lie  in  the  middle  line  of  the 
body  and  are  divisible  into  similar  right  and  left  halves ; 
the  vertebrae  are  good  examples. 

All  bones  are  covered  by  periosteum  except  where  they 
enter  into  the  formation  of  a  joint,  but  in  the  human 
body  only  the  long  bones  possess  a  medullary  cavity  con- 
taining yellow  marrow.  The  rest  are  filled  up  by  spongy 
bone,  covered  by  a  thin  layer  of  dense,  and  have  red  mar- 
row in  their  spaces. 

The  histology  oi  bone. — The  microscope  shows  that 
compact  bone  is  only  so  to  the  naked  eye  ;  even  a  hand 
lens  shows  minute  holes  in  it;  it  but  differs  from  spongy 
bone  in  the  fact  that  its  cavities  are  much  smaller,  and  the 
hard  bony  plates  between  them  thicker,,  It  a  thin  trans- 
verse section  of  the  shaft  ot  long  bone  (Fig.  23)  be  exam- 
ined with  a  microscope  magnifying  about  twenty  diameters, 
even  its  densest  part  will  be  seen  to  show  numerous  open- 
ings which  become  gradually  larger  near  the  medullary 

What  is  a  long  bone?  Give  examples.  A  tabular  bone?  Exam- 
ples. A  short  bone?  Examples.  An  irregular  bone?  Examples. 

With  what  is  most  of  the  surface  of  bones  covered?  Where  is  the 
periosteum  absent?  What  bones  contain  yellow  marrow?  What  do 
the  others  contain? 

Does  compact  bone  contain  any  cavities?  How  may  these  be 
seen?  How  does  it  differ  from  spongy  bone?  What  is  seen  when  a 
thin  slice  of  bone  is  magnified  twenty  iimes?  Where  do  the  apertures 
in  it  become  larger? 


THE    HUMAN    BODY. 


i 


cavity  and  pass  insensibly  into  the  spaces  ot   the  spongy 
bone  around  it.     These  openings  are  the  cross  sections  of 


Fio.  23.— A,  a  transverse  section  oi  the  ulna,  natural  size  ;  showing  the  medul- 
lary cavity.    B\  the  more  deeply  shaded  nart  of  A  magnified  twenty  diameters. 

tubes  known  as  the  Haversian  canals,  which  run  all 
through  the  bone,  the  majority  of  them  in  the  direction  of 
its  long  axis,  though  numerous  cross  branches  unite  them. 
The  outermost  Haversian  canals  open  on  the  surface  of 
the  bone  beneath  the  periosteum ;  from  there  blood-ves- 
sels pass  in,  and,  traversing  the  whole  bone  in  these  chan- 
nels, convey  materials  for  its  growth  and  nourishment. 


What  are  the  Haversian  canals?  Where  do  the  outer  ones  open? 
What  enters  them?  Where  do  tiie  blood-vessels  of  a  bone  run? 
What  do  they  carry  n 


ffiSTOLOGY    OP   BOflE. 


53 


Around  each  Haversian  canal  is  a  series  of  plates  or 
^  each  canal  and  its  lamellae  forming  an  Haversian 
system;  the  entire  bone  is  made  up  of  a -number  of  such 
systems,  with  the  addition  of  a  few  lamellae  lying  in  the 
corners  between  them,  and  some  which  run  around  the 
whole  bone  on  its  outer  surface.  In  the  spongy  bone  the 
Haversian  canals  are  very  large,  containing  red  marrow  as 
well  as  blood-vessels,  and  the  lamellae  around  each  are  few 
in  number. 


FIG.  24.— A  small  piece  of  bone,  ground  very  thin  and  highly  magnified. 

If  a  bit  of  bone  be  still  more  magnified  (Fig.  24)  we 
find  that  very  small  cavities  lie  between  the  lamellaB ;  they 

"What  lies  around  each  Haversian  canal?  What  is  an  Haversian 
system?  Of  what  does  a  bone  consist  in  addition  tc  Haversian  sys- 
tems? Are  the  Haversian  canals  comparatively  large  or  small  in 
spongy  bone?  What  do  the  spaces  of  spongy  bone  contain  in  addi- 
tion to  blood-vessels? 

What  spaces  lie  between  the  lamella}  of  an  Haversian  system? 


54  THS   SUM  AN  BODY. 

are  called  lacuna;  from  eacli  lacuna  radiate  many  ex- 
tremely fine  tubes,  the  canaliculi,  so  tnat  each,  lacuna  with 
its  canaliculi  looks  something  like  a  small  animal  with  a 
great  many  legs.  The  innermost  canaliculi  open  into  the 
Haversian  canal  of  the  system  to  which  they  belong,  and 
those  of  various  lacunae  communicate  with  one  another,  so 
that  a  set  of  passages  is  provided  through  which  liquid 
which  transudes  from  the  blood-vessel  in  the  ilaversian 
canal  can  ooze  all  .through  the  bone. 

In  a  living  bone  a  nucleated  cell  lies  in  each  lacuna. 
These  cells,  the  lone  corpuscles,  are  the  remnants  of  those 
which  made  the  bone,  ail  whose  hard  parts  are  but  in- 
tercellular substance:  a  sort  of  skeleton  is  made  by  ea'ch 
cell  around  itself,  and  this  adheres  to  the  skeletons  of  the 
rest,  and  thus  the  whole  bone  is  built. 

Chemical  composition  of  bone. — Apart  from  the  bone 
corpuscles  and  the  soft  contents  of  the  Ilaversian  canals 
and  of  the  spaces  of  the  cancellated  bone,  the  hard  bony 
substance  proper  is  composed  of  animal  and  mineral  mat- 
ters so  intimately  combined  that  the  smallest  distinguish- 
able bit  of  bone  contains  both.  The  mineral  matters  give 
the  bone  its  hardness  and  stiffness,  and  form  about  two- 
thirds  of  its  weight  when  dried.  They  may  be  removed 
by  soaking  the  bone  in  diluted  muriatic  acid.*  and  the 

What  radiate  irom  the  lacunae?  into  wnat  do  the  innermost 
canaliculi  of  an  Haversian  system  open?  How  is  nourishing  liquid 
from  the  blood  carried  throughout  a  bone? 

What  lies  in  each  lacuna  of  a  living  bone?  What  are  the  Done 
corpuscles?  What  is  the  hard  part  of  bon^y  How  is  a  whole  bone 
made  up? 

Of  what  primary  constituents  is  bone  composed?  Is  there  any 
fragment  of  bone  that  does  not  contain  both?  What  qualities  do  its 
mineral  parts  give  to  a  bone?  How  much  of  a  dry  bone  consists  of 
mineral  matter?  How  may  the  mineral  parts  be  removed? 


*  Add  a  couole  of  ounces  of  Muriacic  acid  to  a  pint  of  water  and  Dlace 


CHEMISTRY    OF   BONE.  55 

animal  or  organic  part  of  the  bone  is  then  left  as  a  tough, 
flexible  mass,  retaining  perfectly  the  shape  of  the  original 
bone. 

When  long  boiled  in  water  the  greater  part  of  the 
animal  portion  of  bone  is  turned  into  gelatine  and  dis« 
solved  in  the  water ;  most  of  the  gelatine  which  we  buy  in 
the  shops  is  obtained  by  boiling  fresh  bones  in  a  closed  ves- 
sel under  a  high  pressure;  the  water  then  gets  much 
hotter  than  when  boiled  in  the  air,  and  dissolves  out  the 
gelatine  more  quickly  ;  when  a  shin  of  beef  is  used  to 
make  soup  the  bones  are  put  m  as  well  as  the  softer  parts, 
and  the  whole  is  kept  boiling  for  hours  so  as  to  get  some 
of  the  gel&tine  out  of  the  bones.  The  animal  matter  of 
bone  gives  it  its  toughness  and  flexibility. 

The  earthy  portion  may  be  obtained  free  from  the 
inimal  by  calcining  a  bone  in  a  bright  fire.  The  residue 
is  a  white  and  very  brittle  mass,  which  retains  perfectly 
the  shape  of  the  ordinal  bone.  It  is  readily  powdered  and 
then  forms  bone  ash,  which  consists  chiefly  of  phosphate 
and  carbonate  of  calcium  ;  most  of  the  phosphorus  of 
commerce  is  obtained  from  it.  If  the  burning  be  imper- 
fect the  animal  matter  is  charred  but  not  altogether  burnt 
away,  and  a  black  mass,  known  as  animal  charcoal  or 
"bone  black,"  is  left. 

What  then  remains  behind?  What  are  its  properties?  Has  it  still 
the  shape  of  the  bone?  What  happens  when  a  bone  is  boiled  for 
hours?  How  is  the  gelatine  of  commerce  obtained?  Why  do  we 
use  bones  in  making  soup?  What  properties  does  its  animal  matter 
confer  on  bones? 

How  may  we  get  the  mineral  part  of  bone  free  from  the  animal? 
What  are  its  properties  when  isolated?  What  is  bone  ash?  From 
what  is  phosphorus  prepared?  What  is  animal  charcoal? 

rib  in  the  mixture  for  four  or  five  days,  hr.ving  previously  scraped  the  bone  quite 
clean.  It  will  be  found  so  flexible  that  a  knot  may  be  tied  on  it;  the  specimen  mjiy 
be  preserved  in  strong  brine  or  dilute  alcohol  from  year  to  year  for  exhibition  to  a 


56  THE    HUMAN   SOD  7. 

Hygiene  of  the  bony  skeleton. — In  early  life  the  animal 
matter  of  the  bones  is  present  in  larger  proportion  than 
later;  hence  the  bones  of  children  are  tougher,  more 
pliable,  and  not  so  easily  broken.  The  bones  of  a  young 
child  are  tolerably  flexible  and  are  capable  of  being  dis- 
torted by  any  long-continued  strain  ;  therefore  children 
should  never  be  placed  on  a  bench  so  high  that  the  feet 
have  no  support  ;  if  this  is  frequently  done  the  thigh 
bones  will  almost  certainly  become  bent  over  the  edge  of 
the  seat  by  the  weight  of  the  lower  legs  and  the  feet,  and 
a  permanent  distortion  may  be  produced.  For  the  same 
reason  it  is  important  that  a  chiP  be  made  to  sit  straight, 
when  writing  or  drawing,  to  avoid  the  risk  of  producing  a 
lateral  curvature  of  the  spinal  column  ;  and  young  chil- 
dren should  not  be  made  to  walk  too  early  lest  they  become 
bow-legged,  their  bones  not  being  rigid  enough  to  bear 
the  weight  of  the  body.  How  easily  the  bones  yield  to 
prolonged  pressure  in  early  life  is  well  illustrated  by  the 
distorted  feet  of  Chinese  ladies  ;  and  by  the  extraordinary 
forms  (Fig.  25)  which  some  races  produce  in  their  skulls 
by  tying  boards  or  bandages  on  the  heads  of  the  children. 
A  distorted  foot,  even  in  the  United  States,  is  no  uncommon 
thing  in  these  days  of  tight  boots  and  high  heels.  The 
latter  are  especially  bad,  as,  instead  of  allowing  the  weight 
of  the  body  to  bear  properly  directly  downwards  on  the 
crown  of  the  arch  of  the  instep,  they  throw  it  forwards, 
and  violently  force  the  fore  part  of  the  foot  into  the  toe  of 

How  do  the  bones  of  children  differ  in  composition  from  those  of 
adults?  How  in  properties?  Why  should  children  have  a  seat  allow- 
ing the  feet  to  be  supported?  Why  should  young  persons  be  taught 
to  sit  erect  while  writing?  What  will  happen  if  young  children  are 
encouraged  to  walk  too  much?  Why?  Give  instances  of  the  readi- 
ness with  which  bones  can  be  distorted  in  early  life.  Whv  are  high- 
heeled  boots  hurtful? 


HYGIENE    OF   SKELETON.  57 

the  boot.  This  not  only  crushes  the  toes  and  leads  to 
deformities,  corns,  and  bunions,  but  makes  the  gait  stiff, 
inelastic  and  ungraceful. 


FIG.  25.— Skull  of  a  child  of  the  tribe  of  Chinook  Indian*  (inhabiting  the  neigh- 
borhood of  the  Columbia  river),  distorted  by  tight  bandaging  so  as  to  assume  the 
shape  considered  elegant  and  fashionable  by  the  tribe. 

In  advanced  life  the  animal  matter  of  the  bones  is 
present  in  deficient  amount,  and  hence  they  are  brittle 
and  easily  broken. 

An  infant  has  its  bones  but  very  imperfectly  hardened 
by  mineral  matter.  Hence  the  great  importance  of  sup- 
plying it  with  food  containing  phosphate  of  lime,  which 
is  the  chief  mineral  constituent  of  bone.  Of  all  common 
articles  of  diet,  milk  contains  most  phosphate  of  lime  : 
hence  one  great  reason  of  its  value  as  a  food  for  children. 

Fracture. — When  a  bone  is  broken  it  is  said  to  be/rac- 
tured ;  when  it  is  a  clean  break  the  fracture  is  simple; 
when  the  bone  is  more  or  less  broken  up  into  bits  on  each 
side  of  the  break  the  fracture  is  comminuted  j  when  the 

"Why  are  the  bones  of  an  old  person  easily  broken?  Why  should 
tnilk  form  part  of  a  child's  diet  ? 

What  is  a  fracture?  A  supple  fracture?  A  comminuted  fracture? 
A.  compound  fracture? 


68  TEE   HUMAN   BODY 

soft  parts  also  are  lacerated,  so  that  there  is  an  opening 
from  the  skin  to  the  broken  bone,  the  fracture  is  com- 
pound. 

Once  a  bone  is  broken  the  muscles  attached  to  it  are 
apt  to  pull  its  ends  out  of  place ;  hence  it  requires  to  be 
"  set,"  and  then  kept  in  position  by  splints  or  bandages;  this 
frequently  needs  much  skill  and  a  thorough  knowledge  of 
the  anatomy  of  the  body.  A  medical  man  should  be  sum- 
moned at  once,  as  the  parts  around  the  break  commonly 
swell  very  rapidly  and  make  the  exact  nature  of  the  frac- 
ture hard  to  detect,  and  also  the  replacement  of  the  dis- 
placed ends  more  difficult. 

Why  does  a  broken  bone  need  "  setting  "?  What  is  the  object  of 
"  splints  "?  Why  should  skilled  assistance  be  obtained  as  soon  as  pos- 
sible after  a  bone  has  been  fractured? 


APPENDIX  TO  CHAPTER  IV. 

When  giving  lessons  on  Chapters  III  and  IV,  it  is  very  desirable 
for  a  teacher  to  have  at  hand  an  articulated  human  skeleton.  This 
may  be  purchased  for  about  $40.00  from  Henry  Ward,  Rochester,  N. 
y.,  and  will  last  for  an  indefinite  number  of  years.  When  the  school 
funds  do  not  permit  the  purchase  of  a  skeleton,  one  can  almost  cer- 
tainly be  borrowed  from  some  medical  man  or  medical  school  for  a 
few  days.  When  there  are  several  public  schools  in  a  city  it  would 
probably  be  possible  to  induce  the  school  commissioners  to  purchase 
a  skeleton  to  be  used  by  the  schools  in  turn. 


PLATE    I. — THE   BOXES,    JOINTS,    AND   LIGAMENTS. 


EXPLANATION  OF  PLATE  I. 

A  front  view  of  an  adult  human  skeleton  to  illustrate  the  mode  in 
which  the  bones  are  connected  together  at  the  different  joints. 

For  the  names  of  the  bones  consult  the  description  of  figure  8, 
which  commences  on  page  26. 

a  Ligaments  of  the  Elbow-Joint. 

6  The  Ligament  which  is  connected  to  the  ventral  surfaces  of  the  bodies  of 

the  Vertebrae. 

e  Ligament  connecting  the  innominate  Bone  to  the  Spine. 
f  Ligament  connecting  the  innominate  Bone  to  the  Sacrum. 
g  The  Ligaments  of  the  Wrist  Joint. 
h  The  Membrane  which  fills  up  the  interval  between  the  two  bones  of  the 

Fore  Arm. 
I  A  similar  Membrane  between  the  two  bones  of  the  Leg,  and,  lower  down, 

Z,  ligaments  of  the  Ankle-Joint. 

fc  A  Membrane  which  fills  up  a  hole  hi  the  Innominate  Bone. 
n  Ligaments  of  the  Knee-joint. 
o  o  Ligaments  of  the  Toes  and  Fingers. 
p  Capsular  (bag-like)  Ligament  of  the  Hip-Joint. 
q  Capsular  Ligament  of  the  bhoulder-Joint. 


CHAPTEE  V. 
JOINTS. 

The  movements  of  the  body  are  brought  about  by  means 
of  soft  reddish  organs  known  as  the  muscles;  the  lean  of 
meat  is  muscle,  so  every  one  knows  what  a  dead  muscle 
looks  like.*  Muscles  have  the  power  of  shortening  with 
considerable  force  ;  when  they  do  so  they  pull  their  ends 
towards  one  another  and  swell  out  in  the  middle ;  in 
other  words,  they  become  shorter  and  thicker.  With  few 
exceptions  the  ends  of  a  muscle  are  attached  to  separate 
bones  f  between  which  a  joint  lies,  and  when  the  muscle 
shortens,  or,  in  physiological  language,  contracts,  it  pro- 
duces movement  at  the  joint.  The  joints  and  muscles  thus 
form  the  chief  motor  apparatuses  of  the  body. 

What  organs  produce  the  movements  of  the  body?  What  is  the 
technical  name  of  the  lean  of  meat?  What  power  do  muscles  pos- 
sess? What  happens  when  they  exert  it?  To  what  are  the  ends  of 
most  muscles  attached?  What"happens  when  the  muscle  contracts? 
Name  the  chief  motor  apparatuses  of  the  body? 

*  In  many  animals  some  muscles  are  much  redder  than  others,  and  it  is  then 
found  that  the  deeper  colored  are  those  which  are  kept  most  constantly  in  use  ;  the 
leg  muscles  of  a  chicken,  for  example,  are  redder  than  those  of  the  wings  and 
breast,  ar.d  as  the  coloring  matter  is  turned  brown  by  heat,  they  form  the  "dark 
"neat"  after  cooking  ;  in  birds  which  fly  a  great  deal  the  breast  muscles  (which 

iefly  move  the  wings)  are  also  dark.  The  heart,  which  is  a  muscle  always  at 
work,  is  deep  red,  even  in  fishes,  most  of  whose  muscles  are  pale. 

t  As  an  example  of  a  muscle  not  attached  to  the  skeleton,  we  may  take  the  orbic- 
ularis  oris,  which  forms  a  ring  around  the  mouth-opening  beneath  the  skin  of  trie 
l^pp  :  when  it  contracts  it  closes  the  mouth,  or  if  it  contracts  more  forcioly  purses 
out  the  lips.  The  orbicularis  palpebrarum  forms  a  similar  ring  around  the  eye 
opening,  andwhen  it  contracts  closes  the  eye. 


60  THE    HUMAN    BODY. 

Joints. — Articulations  which  permit  of  movement  by 
the  gliding  of  one  bone  over  another  are  called  'joints  ;  all 
are  constructed  on  the  same  general  plan,  though  the 
range  and  direction  of  movement  permitted  are  different  in 
different  joints.  As  an  example  we  may  take  the  hip- 
joint,  a  section  through  which  is  represented  in  Fig.  26. 


FIG.  26. — Section  through  the  hip-joint. 

On  the  outer  side  of  the  os  innominatum  (s,  Fig.  8) 
is  a  deep  hollow,  the  acetabulum,  which  receives  the  upper 
end  of  the  thigh-bone.  The  acetabulum  is  lined  by  a  thin 
layer  of  cartilage,  with  an  extremely  smooth  surface,  and 
its  cavity  is  also  deepened  by  a  cartilaginous  rim.  The 
upper  end  of  the  femur  consists  of  a  nearly  spherical  head, 
borne  on  a  narrower  neck  ;  this  head  is  covered  by  car- 
tilage, and  rolls  smoothly  in  the  acetabulum  like  a  ball  in 

What  is  a  joint?    How  do  joints  differ?    Describe  the  hip-joint. 


HIP-JOINT.  61 

a  socket.  If  the  hard  bones  came  into  direct  contact  they 
would  be  apt  to  chip  one  another  when  a  sudden  move- 
ment was  made,  especially  if  the  hip-joint  were  so  far  bent 
as  to  knock  the  thigh-bone  against  the  rim  of  the  acetabu- 
lum;  the  elastic  and  yielding  cartilage  forms  a  protecting 
cushion  between  the  bones  and  prevents  this. 

To  keep  the  bones  in  place  and  limit  the  range  of 
movement,  ligaments  pass  from  one  to  the  other  ;  they  are 
composed  of  connective  tissue,  are  extremely  pliable  but 
cannot  be  stretched,  and  are  very  tough  and  strong.  One 
is  the  capsular  ligament,  which  forms  a  bag  all  round  the 
joint,  and  another  is  the  round  ligament,  L.  T.,  Fig.  26, 
which  passes  from  the  rim  of  the  acctabulr.m  to  the  head 
of  the  femur  ;  from  the  rim  of  the  socket  it  passes  to 
the  center  of  the  acetajbulum  along  a  groove  in  the  bone, 
and  then  turns  out  to  be  fixed  to  the  thigh-bone. 

Covering  the  inside  of  the  capsular  lignment  and  con- 
tinued over  the  cartilages  of  the  joint  is  the  synovial  mem- 
brane, very  thin  and  composed  of  a  layer  of  flat  cells. 
This  pours  out  into  the  joint  a  very  small  quantity  of 
synovial  liquid,  which  is  somewhat  like  the  white  of  a  raw 
egg  in  consistency,  and  plays  the  part  of  the  oil  moisten- 
ing those  surfaces  of  a  machine  which  glide  over  one 
another  ;  it  lubricates  the  joint  and  enables  all  to  run 
smoothly  and  with  but  little  friction. 

In  the  natural  state  of  the  parts  the  synovial  membrane 

What  is  the  use  of  the  cartilage  lining  the  bones  which  move  over 
one  another  in  n  joint? 

What  is  the  use  of  ligaments?  Of  what  are  they  composed? 
What  are  their  properties?  Name  some  ligaments  of  the  hip- joint. 
Where  does  the  nsipsulnr  lisrn  merit  lie?  Where  the  round  ligament? 
What  membrane  lines  the  joint?  Of  what  is  it  composed?  What 
does  it  ponr  into  the  joint?  What  is  synovial  liquid  like?  What  is 
its  use?  Illustrate  by  an  example. 


62  TBS   HUMAN   BODY. 

on  the  head  of  the  thigh-bone  lies  close  against  that  lining 
the  acetabulum,  so  that  practically  there  is  no  cavity  left 
in  the  joint.  This  close  contact  is  not  maintained  by  the 
ligaments  (which,  are  much  too  loose,  and  serve  mainly  to 
prevent  such  excessive  movement  as  might  roll  the  femur 
quite  out  of  its  socket),  but  by  the  many  strong  muscles 
which  pass  between  pelvis  and  thigh-bone  and  hold 
both  firmly  together.  In  addition,  the  pressure  of  the 
atmosphere  is  transmitted  by  the  skin  and  muscles  to 
the  exterior  of  the  air-tight  joint,  and  helps  to  keep  its 
surfaces  together.  If  all  the  muscles  be  cut  away  from 
around  the  hip-joint  of  a  dead  body,  it  is  found  that  the 
head  of  the  femur  is  still  held  in  its  place  by  the  pressure 
of  the  air  ;  and  so  firmly  that  the  weight  of  the  whole 
limb  will  not  draw  it  out ;  but  if  a  hole  be  pierced  into  the 
bottom  of  the  acetabulum,  and  air  be  thus  let  into  the 
joint,  then  the  thigh-bone  falls  out  of  place  as  far  as  the 
ligaments  will  let  it. 

In  all  joints  we  find  the  same  essential  parts ;  bones, 
articular  cartilages,  synovial  membrane,  synovial  liquid, 
and  ligaments.* 

Ball  and  socket  joints. — Such  a  joint  as  that  at  the  hip 

Is  there  in  health  any  definite  space  between  the  bones  of  the  hip- 
joint?  What  is  the  chief  use  of  the  ligaments?  How  are  the  bones 
held  together?  What  in  addition  to  muscles  helps  to  keep  the  bones 
of  the  joint  in  contact?  Describe  an  experiment  illustrating  the 
effect  of  atmospheric  pressure  in  keeping  the  bones  together? 

What  essential  parts  are  found  in  all  "joints? 

What  is  such  a  joint  as  the  hip- joint  called? 


*  The  structure  of  joints  can  be  readily  seen  in  those  of  a  fresh  calf's  or  sheep's 
foot.  The  synovial  membrane  is  so  thin  and  ?o  closely  adherent  to  the  parts  it  lines 
that  a  microscope  is  needed  for  its  demonstration  ;  but  all  the  other  parts  are  readily 
made  out. 


BALL    AND    SOCKET   JOINf®.  63 

is  called  a  ball  and  socket  joint,  and  allows  of  a  greater 
variety  of  movement  than  any  other  kind.  Through 
movements  taking  place  at  it  the  thigh  can  (1)  be  flexed, 
that  is,  bent  so  that  the  knee  approaches  the  chest,  and 
(2)  extended  or  straightened  again ;  it  can  (3)  be  abducted 
so  that  the  knee  is  moved  away  from  the  middle  line  of 
the  body,  and  (4)  adducted  or  brought  back  again;  by 
movement  at  the  hip  the  limb  can  also  (5)  be  circum- 
ducted,  so  that,  with  knee  and  ankle  joints  held  rigid,  the 
whole  leg  is  made  to  describe  a  cone,  of  which  the  apex  is 
at  the  hip-joint  and  the  base  at  the  foot ;  and  finally  (6) 
rotated  so  that  the  whole  limb  can  be  rolled  to  and  fro  a 
little  about  its  own  long  axis.  All  ball  and  sockets  joints 
allow  all  these  movements  to  a  greater  or  less  extent. 

Another  important  ball  and  socket  joint  is  that  be- 
tween the  upper  end  of  the  humerus  and  the  hollow 
(glenoid  fossa)  near  the  upper  outer  corner  of  the  shoulder 
blade.  The  glenoid  fossa  being  much  shallower  than  the 
acetabulum  the  range  of  movement  possible  at  the  shoulder, 
is  greater  than  at  the  hip- joint. 

Hinge-joints. — In  this  form  the  bony  cavities  and  pro- 
jections are  not  spherical,  but  are  grooved  and  ridged  so 
that  one  bone  can  glide  over  the  other  in  one  plane  only, 
to  and  fro,  like  a  door  on  its  hinges. 

The  knee  is  a  hinge-joint ;  it  can  only  be  bent  and 
straightened,  in  technical  language,  flexed  and  extended. 

What  kind  of  joints  allow  of  the  freest  movement?  What  is 
meant  by  flexion  of  the  thigh?  By  extension?  By  abduction?  By 
adduction?  By  circumduction?  By  rotation?  What  movements 
do  all  ball  and  socket  joints  permit? 

What  sort  of  a  joint  is  that  at  the  shoulder?  Why  is  more  move- 
ment possible  at  it  than  at  the  hip-joint? 

What  is  a  hinge- joint?    Give  an  illustration. 

Name  other  hinge-joints. 


64  THE    HUMAN  BODY. 

Between  the  phalanges  of  the  fingers  we  find  also  hinge- 
joints  ;  another  is  found  between  the  lower  jaw  and  the 
cranium,  allowing  us  to  open  and  close  the  mouth. 
The  latter  is  not,  however,  a  perfect  hinge-joint  ;  it  per- 
mits also  of  slight  lateral  movements,  and  a  gliding  motion 
by  which  the  lower  jaw  can  be  thrust  forward  so  as  to 
bring  the  lower  range  of  teeth  outside  the  upper.* 

Pivot-joints. — In  this  form  one  bone  rotates  about 
another.  A  good  example  is  found  between  the  first  and  sec- 
ond cervical  vertebrae  (Figs.  13, 14).  The  odontoid  process 
of  the  axis  reaches  up  into  the  neural  arch  of  the  atlas, 
and,  kept  in  place  there  by  the  transverse  ligament  which 
does  not  let  it  press  against  the  spinal  cord,  forms  a  pivot 
around  which  the  atlas  rotates,  carrying  the  skull  with  it 
when  we  turn  the  head  to  right  or  left. 

A  more  complicated  kind  of  pivot-joint  is  found  in  the 
forearm.  Lay  the  forearm  and  hand  flat  on  a  table,  palm 
uppermost ;  without  moving  the  shoulder-joint  at  all  the 
hand  can  then  be  turned  over  so  that  its  back  is  upward. 
In  this  movement  the  radius,  which  carries  the  hand, 
crosses  over  the  ulna.  When  the  palm  is,  turned  up 
(summation)  the  radius  and  ulna  are  parallel  (Fig.  27,  A), 
and  the  radius  on  the  outside ;  place  a  finger  of  the  other 

Is  the  joint  of  the  lower  jaw  with  the  skull  a  perfect  hinge  joint? 
What  movements  can  take  place  at  it? 

What  is  a  pivot- joint?  Name  an  instance  from  the  spinal  column. 
Describe  the  joint  between  atlas  and  axis.  What  happens  to  the  head 
when  the  atlas  rotates  on  the  odontoid  process  of  the  axis? 

Where  do  we  find  another  kind  of  pivot-joint?  Illustrate  its 
action.  What  happens  when  we  turn  the  hand  so  that  the  palm 
instead  of  being  up  shall  be  down?  How  can  we  observe  the  relative 
change  in  position  of  radius  and  ulna  while  making  this  movement? 

*  The  object  of  these  minor  movements  is  to  allow  us  to  chew  our  foo<1 ;  in  car- 
nivora,  as  cats,  which  bite,  but  do  not  chew,  the  lower  jaw  forms  a  perfect  hinge' 
joint  with,  the  cranium. 


DISLOCATIONS. 


65 


hand  on  it  near  the  wrist,  and  then  turn  the  hand  over  ; 
the  lower  end  of  the  radius  will  be -found  to  cross  over  the 
ulna  and  to  be  on  its  inner  side  (Fig.  27,  B),  when  tho 
movement  is  completed  ;  in  this 
position  the  hand  is  said  to  be 
in  pronation. 

The  lower  end  of  the  hume- 
rus  (Fig.  21)  has  a  large  artic- 
ular surface  ;  on  the  inner  two- 
thirds  of  this,  Ir,  the  ulna  fits, 
and  the  grooves  and  ridges  of 
the  bones  interlocking  form  a 
hinge -joint,  allowing  us  only  to 
bend  or  straighten  the  elbow- 
joint.  The  radius  fits  on  the 
rounded  outer  third,  Cpl,  and 
rotates  there  when  the  hand 
is  turned  over,  the  ulna  form- 
ing a  fixed  bar  around  which  it 
moves.  B  A 

n-lirKno-   imnfc    no  a   vnln    i^ov         FlG    27-— A,  arm  in  Bupination ; 

Witting  joints  as  a  rule  pei-  B  arm  In  pronati0n;  a;fiumenw; 
mit    of    but    little    movement.    jR'radius;  ^ulna' 
Examples  are  found  between  the  closely-packed  bones  of 
the  carpus  and  tarsus  (Fig.  19),  which  slide  a  little  over 
one  another  when  subjected  to  pressure. 

Dislocations. — When  a  bone  is  displaced  at  a  joint  or 
dislocated,  the  ligaments  are  more  or  less  torn  and  other 

What  movement  is  allowed  between  ulna  and  humerus?  What 
between  radius  and  huraerus?  Around  what  does  the  radius  rotate 
when  we  turn  the  hand  over? 

Do  gliding  joints  allow  free  movement?  Give  instances  of  gliding 
joints. 

What  is  a  dislocation?  What  parts  are  injured  when  a  joint  is 
dislocated? 

5 


66  THE    HUMAN    BODY. 

surrounding  soft  parts  injured.  This  generally  leads  to 
inflammation  and  swelling,  which  make  it  difficult  to  find 
out  in  wlnit  direction  the  hono  has  been  displaced,  and 
also  greatly  add  to  the  difficulty  of  replacing  it,  or,  in  sur- 
gical language,  of  reducing  the  dislocation.  The  muscles 
attached  to  it  are,  moreover,  apt  to  pull  the  dislocated 
bone  more  and  more  out  of  place.  Medical  aid  should 
therefore  be  obtained  as  soon  as  possible  ;  in  most  cases 
the  reduction  of  a  dislocation  can  only  be  attempted  with 
safety  by  one  who  knows  the  forms  of  the  bones  and  pos- 
sesses sufficient  anatomical  knowledge  to  recognize  the 
direction  of  the  displacement.* 

A  sprain  is  an  injury  to  a  joint,  accompanied  by  strain- 
ing, twisting,  or  tearing  of  the  ligaments,  but  without  dis- 
location of  the  bones.  A  sprained  joint  should  get  imme- 
diate and  complete  rest,  continued  for  weeks  if  neces- 
sary ;  if  there  be  much  swelling  or  continued  pain,  medical 
advice  should  be  obtained.  Perhaps  a  greater  number  of 
permanent  injuries  result  from  neglected  cprains  than  from 
broken  bones. 


What  results  from  this  injury  ?  What  is  meant  by  "  reducing  a 
dislocation  ?"  Why  should  medical  aid  be  obtained  as  soon  as  possi- 
ble after  a  joint  has  been  dislocated  ? 

What  is  a  sprain  ?  How  should  a  sprained  joint  be  treated  ? 
What  should  be  done  at  once  if  there  is  much  swelling  or  continued 
pain  ?  Are  neglected  sprains  apt  to  lead  to  permanent  injury  ? 

*  Dislocations  of  the  fingers  can  usnaily  be  reduced  by  strong  pulling,  aided  by  a 
little  pressure  on  the  parts  of  the  bones  nearest  the  joint.  The  reduction  of  a  dis- 
location of  the  thumb  is  much  more  difficult,  and  can  rarely  be  accomplished  with- 
out skilled  assistance. 


EXPLANATION  OF  PLATE  II. 

A  view  of  the  muscles  situated  on  the  front  surface  of  the  body, 
seen  in  their  natural  position.  It  must  be  understood  that  beneath 
these  muscles  many  others  are  situated,  which  cannot  be  represented 
in  the  figure. 

Muscles  of  the  Face,  Head,  and  Neck: 

1.  Muscle  of  the  Forehead.    This,  together  with  a  muscle  at  the  back  of  the 

head,  has  the  power  of  moving  the  scalp. 

2.  Muscle  that  closes  the  Eyelids.     The  muscle  that  raises  the  upper  eyelid 

so  as  to  open  the  eye,  is  situated  within  the  orbit,  and  consequently 
cannot  be  seen  in  this  figure. 

3.  4,  5.  Muscles  that  raise  the  Upper  Lip  and  angle  of  the  Mouth. 

6,  7.  Muscles  that  depress  the  Lower  Lip  and  angle  of  the  Mouth.  By  the 
action  of  the  muscles  which  raise  the  upper  lip,  and  those  that  depress 
the  lower  lip,  the  lips  are  separated. 

8.  Muscle  that  draws  the  Lips  together. 

9.  Muscle  of  the  Temple  (Temporal  Muscle). 

10.  Masseter  Muscle.    9  and  10  are  the  two  chief  muscles  of  mastication,  for 

when  they  contract,  the  movable  lower  jaw  is  elevated,  so  as  to  crush 
the  food  between  the  teeth  in  the  upper  and  lower  jaws. 

11.  Muscle  that  compresses  the  Nostril.    Close  to  its  outer  side  is  a  small 

muscle  that  dilates  the  nostril. 

12.  Muscle  that  wrinkles  the  Skin  of  the  Neck,  and  assists  in  depressing  the 

lower  jaw. 

13.  Muscle  that  assists  in  steadying  the  Head,  and  also  in  moving  it  from  side 

to  side. 

14.  Muscles  that  depress  the  Windpipe  and  Organ  of  Voice.    The  muscles 

that  elevate  the  same  parts  are  placed  beneath  the  lower  jaw,  and  can- 
not be  seen  in  the  figure. 

Muscles  that  connect  the  upper  extremity  to  the  trunk.  Portions 
of  four  of  these  muscles  are  represented  in  the  figure,  viz. : 

15.  Muscle  that  elevates  the  Shoulder.    Trapezius  Muscle. 

17.  Great  Muscle  of  the  Chest,  which  draws  the  Arm  in  front  of  the  Chest 

(Great  Pectoral  Muscle). 

18.  Broad  Muscle  of  the  Back,  which  draws  the  Arm  downwards  across  the 

back  of  the  Body  (Latissimus  Dorsi). 

19.  Serrated  Muscle  extends  between  the  Ribs  and  Shoulder-blade,  and  draws 

the  shoulder  forwards  and  rotates  it,  a  movement  which  takes  place  in 
the  elevation  of  the  arm  above  the  head  (Serratus  magnus). 


At  the  lower  part  of  the  trunk,  on  each  side,  may  be  seen  the  large 
muscle  which,  from,  the  oblique  direction  of  its  fibres,  is  called, 

20.  Outer  Oblique  Muscle  of  the  Abdomen. 

Several  muscles  lie  beneatli  it.     The  outline  of  one  of  these, 

21.  Straight  Muscle  of  the  Abdomen,  may  be  seen  beneath  the  expanded 

tendon  of  insertion  of  the  oblique  muscle.  These  abdominal  muscles, 
by  their  contraction,  possess  the  power  of  compressing  the  contents  of 
the  abdomen. 

Muscles  of  the  upper  extremity. 
16.  Muscle  that  elevates  the  Arm  (Deltoid  Muscle). 

22.  Biceps  or  Two-headed  Muscle  (see  also  page  70). 

23.  Anterior  Muscle  of  the  Arm.    This  and  the  Biceps  are  for  the  purpose  of 

bending  the  Fore -Arm 

24.  Triceps,  or  Three-headed  Muscle.    This  counteracts  the  last  two  muscles, 

for  it  extends  the  Fore-arm. 

25.  Muscles  that  bend  the  Wrist  and  Fingers,  and  pronate  the  Fore-arm  and 

Hand — that  is,  turn  the  Hand  with  the  palm  downwards.  They  are 
called  the  Flexor  and  Pronator  Muscles. 

26.  Muscles  that  extend  the  Wrht  and  Fingers,  and  supinate  the  Fore-arm 

and  Hand— that  is,  turn  the  Hand  with  its  palm  upwards.  They  are 
called  the  Extensor  and  Supinator  Muscles. 

27.  Muscles  that  constitute  the  ball  of  the  Thumb.    They  move  it  in  different 

directions. 

28.  Muscles  that  move  the  Little  Finger. 

Muscles  which  connect  the  lower  extremity  to  the  pelvic  bone. 
Several  are  represented  in  the  figure. 

29.  Muscle  usually  stated  to  have  the  power  of  crossing  one  Leg  over  the 

other,  hence  called  the  Tailor's  Muscle,  or  Sartorius;  its  real  action  is 
to  assist  in  bending  the  knee. 

30.  Muscles  that  draw  the  Thighs  together  (Adductor  Muscles). 

31.  Muscles  that  extend  or  straighten  the   Leg   (Extensor    Muscles).    The 

muscles  that  bend  the  lesr  are  placed  on  the  back  of  the  thigh,  so  that 
they  cannot  be  seen  in  the  figure. 

Muscles  of  the  leg  and  foot: 

32.  Muscles  that  bend  the  Foot  upon  the  Leg.  and  extend  the  Toes. 

33.  Muscles  that  raise  the  Heel— these  form  the  prominence  of  the  calf  of  the 

Leg. 

34.  Muscles  that  turn  the  Foot  outwards. 

35.  A  band  of  membrane  which  retains  in  position  the  tendons  which  pass 

from  the  leg  to  the  foot. 

36.  A  short  muscle  which  extends  the  Toes. 

The  muscles  which  turn  the  foot  inwards,  so  as  to  counteract  the 
last  named  muscles,  lie  beneath  the  great  muscles  of  the  calf,  which 
consequently  conceal  them.  The  foot  possesses  numerous  muscles, 
which  act  upon  the  toes,  so  as  to  move  them  about  in  various  direc- 
tions. These  are  principally  placed  on  the  sole  of  the  foot,  so  that 
they  cannot  be  seen  in  the  figure.  Only  one  muscle,  36,  which  assists 
in  extending  the  toes,  is  placed  on  the  back  of  the  foot. 


PLATE    II.— THE    SUPERFICIAL   MUSCLKS   OF   THE    FRONT   OF   THE    BODY. 


CHAPTER   VI. 
THE  MUSCLES. 

The  muscles  of  the  human  body  are  more  than  five  hun- 
dred in  number ;  they  vary  very  much  in  size  ;  from  tiny 
ones  not  an  inch  long,  in  the  voice-box,  to  that  on  the  front 
of  the  thigli  (29,  PI.  II.),  which  passes  from  the  pelvis  to 
the  tibia,  and  is  eighteen  inches  or  more  in  length.  What- 
ever their  size,  muscles  present  a  similar  structure  and 
possess  the  same  properties,  their  various  uses  depending 
on  the  different  directions  in  which  they  pull,  and  the 
different  things  they  pull  upon.  In  addition  to  their 
primary  function  of  moving  the  body  the  muscles  give  it 
roundness  and  shapeliness  ;  they  also  help  to  enclose  cavi- 
ties, as  the  abdomen  and  the  mouth  ;  and  they  hold  bones 
together  at  joints. 

The  parts  of  a  muscle. — In  its  commonest  form  a  muscle 
consists  of  a  red  soft  central  part,  called  its  belly,  which 
tapers  towards  each  end  and  there  passes  into  one  or  more 
dense  white  cords,  made  of  connective  tissue  and  called 
tendons  ;  the  tendons  attach  the  muscle  to  parts  of  the 

About  how  many  muscles  are  there  in  the  body?  Between  what 
limits  do  they  differ  in  size?  In  what  respects  do  all  muscles  resem- 
ble one  another?  How  are  their  different  uses  determined?  What 
functions  do  muscles  fulfill  besides  moving  the  body  and  its  parts? 
Give  examples. 

What  is  the  most  usual  structure  of  a  muscle?  What  is  the  use  of 
tendons  ? 

[Wl 


68 


2  HE    HUM  Ay   BOJDT. 


skeleton.*  In  Fig.  28  are  shown  some  of  the  muscles  of 
the  arm.  Their  anatomical  names 
we  need  not  trouble  about ;  but  it 
will  be  seen  that  some  (8,  11,  12) 
pass  from  arm  to  forearm:  others, 
as  16,  15, 14,  13, 17,  18,  start  from 
the  forearm  bones  and  pass  to  the 
bones  of  the  hands ;  near  the 
wrist  they  end  in  slender  tendons, 
which  are  bound  down  into  place 
by  a  stout  cross  band  of  con- 
nective tissue.  The  skin  has 
been  dissected  away  from  the  back 
of  the  middle  finger  to  show  the 
endings  of  tendons  on  its  pha- 
langes. 

The    belly    of   a    muscle  is  its 

What    portion  of    a  muscle  is   its 
working  part? 


FIG.  28.— The  muscles  on  the 
back  of  the  hand,  forearm,  and 
lower  half  of  the  arm,  as  ex- 
posed on  dissecting  away  the 
ekm 


*  The  parts  of  a  muscle  may  readily  be  seen 
in  that  which  forms  the  calf  of  a  frog's  leg. 
Put  a  teaspoonful  of  ether  in  a  quart  of  water, 
immerse  a  frog  in  it,  and  cover  the  vessel.  In  a 
minute  the  animal  will  be  quite  insensible  ;  ita 
head  can  then  be  cut  off  and  its  spinal  cord 
destroyed  by  running  a  pin  along  it,  without 
causing  the  animal  any  pain.  Now  make  cir- 
cular cuts  through  the  skin  at  the  top  of  the 
thighs  and  then  peel  the  ekin  off  like  a  pair  of 
hose  :  it  will  come  quite  easily  except  about  the 
knee-joint,  where  it  may  be  necessary  to  carefully 
divide  one  or  two  tough  bands.  On  the  skinned 
leg  many  muscles  will  be  observed,  and  the  long 
slender  tendons  which  run  to  the  toes.  The 
calf  muscle  will  be  seen  to  end  below  in  a 
strong  tendon  near  the  heel.  If  this  be  divided, 
and  the  muscle  turned  upwards,  it  will  be  found 
to  have  at  the  upper  end  of  its  thick  rounded 
belly  a  pair  of  short  tendons. 


THE    PARTS    OF   A    MUSCLE.  69 

working  part ;  nerves  from  the  brain  or  spinal  cord  enter 
it,  and  when  its  nerve  is  excited,  whether  involuntarily  or 
by  what  we  call  an  act  of  "  will,"  the  belly  contracts;  it 
forcibly  changes  its  shape  so  as  to  become  shorter  and 
thicker.  In  so  doing  it  drags  on  the  tendons,  which  are 
passive  inextensible  cords  and  transmit  the  pull  to  the 
parts  to  which  they  are  attached. 

The  tendons  are  often  quite  long,  as  for  example  those 
of  many  of  the  muscles  moving  the  fingers  (Fig.  28), 
whose  bellies  are  in  the  forearm.  The  belly  of  the  common 
extensor  muscle  of  the  fingers  (14,  Fig.  28)  is  seen,  for 
example,  to  be  in  the  upper  half  of  the  forearm,  and  to 
end  above  the  wrist  in  a  single  tendon  which  divides  up 
into  strips  which  run  along  the  back  of  each  finger ;  the 
muscles  which  straighten  the  thumb,  17,  18  and  19,  are 
also  seen  to  have  long  slender  tendons. 

Where  a  muscle  passes  over  a  joint  it  is  usually  reduced 
to  a  narrow  tendon  ;  the  bulky  bellies,  if  they  lay  there, 
would  make  the  joints  clumsy  and  limit  their  mobility. 
Some  muscles  pass  over  two  joints  and  can  produce  move- 
ment at  either;  the  biceps  of  the  arm,  fixed  above  to  the 
scapula  and  below  to  the  radius,  can  produce  movement  at 
either  the  elbow  or  the  shoulder  joint. 

The  shortening  of  a  muscle  when  it  contracts  is  shown 
by  the  movement  which  it  causes  ;  the  thickening  may  be 

What  enters  the  belly  of  a  muscle?  How  is  the  nerve  of  a  muscle 
excited?  What  happens  when  the  nerve  is  excited?  What  results 
from  the  contraction  of  the  belly  of  a  muscle? 

Are  tendons  ever  long?  Describe  the  common  extensor  muscle  of 
the  fingers  and  its  tendons.  Describe  the  position  and  length  of  ten- 
dons of  the  muscles  which  extend  the  thumb. 

What  happens  to  a  muscle  when  it  passes  over  a  joint?  Why? 
Name  a  muscle  which  crosses  two  joints.  At  what  joints  can  the 
biceps  muscle  of  the  arm  produce  movement? 

How  is  the  shortening  of  a  contracting  muscle  shown? 


70  THE    HUMAN   BODY. 

seen  and  felt  on  the  biceps  in  front  of  the  humerus  when 
the  elbow  is  bent,  or  in  the  ball  of  the  thumb  when  that 
digit  is  moved  so  as  to  touch  the  little  finger  ;  when  a  muscle 
contracts  its  belly  may  also  be  felt  to  grow  harder.  The 
swelling  and  hardening  of  a  contracted  muscle  are  daily 
illustrated  when  one  schoolboy  invites  another  to  feel  his 
"biceps." 

The  Origin  and  Insertion  of  Muscles. — Almost  invaria- 
bly that  part  of  the  skeleton  to  which  one  end  of  a  mus- 


FIG.  29.— The  biceps  muscle  and  the  arra-bones,  to  illustrate  how,  under  ordi- 
nary circumstances,  the  elbow  joint  is  flexed  when  the  muscle  contracts. 

cle  is  fixed  is  more  easily  moved  than  that  part  on  which 
it  pulls  by  its  other  tendon  ;  the  less  movable  attachment 
is  the  origin,  the  other  the  insertion  of  the  muscle.  Tak- 
ing the  biceps  of  the  arm,  we  find  that  when  the  belly  of 
the  muscle  contracts  and  pulls  on  its  upper  and  lower 
tendons,  the  result  is  commonly  that  only  the  forearm  is 
moved,  the  elbow  joint  being  bent  as  shown  in  Fig,  29. 

How  may  its  thickening  be  recognized?  What  change  besides 
thickening  and  shortening  occurs  in  the  belly  of  a  contracted  muscle? 
Give  an  example. 

What  is  meant  by  the  origin  of  a  muscle?  What  by  the  insertion? 
Give  an  example. 


VARIETIES     OF     MUSCLES.  71 

The  shoulder  is  so  much  more  firm  that  it  serves  as  a 
fixed  point,  and  so  that  end  of  the  biceps  is  the  origin  of 
the  muscle,  and  the  radial  attachment  its  insertion.  The 
distinction  is,  however,  only  relative  :  if  the  radius  were 
held  immovable  the  muscle  would  move  the  shoulder 
towards  the  radius,  instead  of  the 
radius  towards  the  shoulder ;  as,  for 
example,  in  going  up  a  rope  "  hand 
over  hand." 

Varieties  of  Muscles. — Many  muscles 
have  the  simple  typical  form  of  a  belly 
tapering  towards  each  end,  as  A,  Fig. 
30  ;  others  divide  at  one  end,  and  are 
called  two-headed,  or  biceps  muscles, 
and  there  are  even  three-headed  or  fe'SftStal 
triceps  muscles.  On  the  other  hand, 


some  muscles  have  no  tendon  at  all  at  r 
one  end,  the  belly  running  right  up  to  the  bone  to  which 
it  is' fixed,  and  some  have  no  tendon  at  either  end.  Some- 
times a  tendon  runs  along  the  side  of  a 
muscle,  and  the  fibres  of  the  latter  are  at- 
tached to  it  obliquely  (B,  Fig.  30)  ;  such 
a  muscle  is  called  penniform  or  feather- 
like,  from  a  fancied  resemblance  to  the  -plQ  37.__A  di- 
vane  of  a  feather  ;  or  a  tendon  may  run  gast 
down  the  middle  of  the  muscle  (C),  which  is  then  called 
bipenniform.  Sometimes  a  tendon  is  found  in  the  mid- 
dle of  the  belly  as  w^ll  as  at  each  end  (Fig.  31)  ;  such  a 

Is  the  origin  of  a  muscle  under  all  circumstances  its  most  fixed 
end?  Give  an  example. 

What  is  the  simple  typical  form  of  a  muscle?  What  is  a  biceps 
muscle?  What  a  triceps?  Have  all  muscles  tendons  at  each  end?  At 
either  end?  Describe  a  penniform  muscle.  A  bipeiiniform. 


72  THE    HUMAN    BODY. 

muscle  is  called  two-bellied  or*  digastric.  Banning  along 
the  front  of  the  abdomen,  from  the  pelvis  to  the  chest; 
on  each  side  of  the  middle  line,  is  a  long  muscle,  the 
straight  muscle  of  the  abdomen  (rectus  abdominis)  ;  it  is 
polygastric,  consisting  of  four  bellies  separated  by  short 
tendons.  Many  muscles  are  not  rounded,  but  form  wide, 
flat  masses,  as  those  which  lie  beneath  the  skin  on  the  sides 
of  the  abdomen. 

How  the  muscles  are  controlled. — Most  of  the  muscles 
of  the  body  are  paired  in  a  double  sense.  In  the  first 
place,  to  nearly  every  one  answers  a  corresponding  muscle 
on  the  opposite  side  of  the  body,*  its  true  mate  ;  in  addi- 
tion, most  are  paired  with,  or  rather  pitted  against,  an 
antagonist ;  for  example,  to  the  biceps  muscle  (Fig.  29) 
which  lies  in  front  of  the  humerus  and  bends  the  elbow 
joint,  corresponds  the  triceps  muscle  which  lies  behind 
the  arm  bone  and  extends  the  elbow  5  when  the  biceps 
contracts  the  triceps  relaxes,  and  vice  versa.  This  orderly 
working  is  carried  out  by  means  of  the  brain  and  spinal 
cord,  which,  through  the  nerves,  govern  the  muscles  and 
regulate  their  activity.  In  convulsions  these  controlling 
organs  are  out  of  gear,  and  the  muscles  are  excited  to  con- 
tract in  all  sorts  of  irregular  and  useless  ways  ;  antagonists 
pulling  against  one  another  at  the  same  moment  the  whole 
body  is  made  rigid. 

A  digastric.  Where  do  we  find  a  polygastric  muscle?  How  is 
the  rectus  ubdominis  muscle  constituted  ?  Where  are  flat  wide 
muscles  found  ? 

In  what  two  ways  are  muscles  paired?  Give  an  example  of  antag- 
onistic muscles.  What  happens  to  the  triceps  when  the  biceps  con- 
tracts? How  is  the  orderly  working  of  the  muscles  guided  and  con- 
trolled? What  parts  are  out  of  working  order  in  a  fit  of  convulsions? 
Why  do  the  limbs  often  become  stiff  in  convulsions? 

'The  single  mnpcles  cross  the  middle  line  and  are  made  up  of  similar  right  and 
left  halves  ;  examples  are  orbicularis  oris  and  the  diaphragm. 


THE    GROSS    STRUCTURE    OF    A    MUSCLE.  73 

The  Gross  Structure  of  a  Muscle. — Each  muscle  is  an 
organ  composed  of  several  tissues.  Its  essential  constitu- 
ent is  a  number  of  fibres  consisting  of  striped  muscular 
tissue*  These  are  supported  and  protected  by  connective 
tissue ;  intertwined  with  blood  and  lymph  vessels,  which 
convey  nourishment  and  carry  off  waste  matters  ;  and 
penetrated  by  nerves  which  govern  their  activity. 

A  loose  sheath  of  connective  tissue,  the  perimysium9 
envelopes  the  whole  muscle  in  a  sort  of  case  ;  from  it 
partitions  run  in  and  sub- 
divide the  belly  of  the  mus- 
cle into  bundles  or  fasciculi 
which  run  from  tendon  to 
tendon,  or  the  whole  length 
of  the  muscle  when  it  has 
no  tendons.  The  coarse- 
ness or  fineness  of  meat  de- 

r»PTirl«  rm    thp    <ai*7P    nf    fViPCP          Fi(J-  32.— A  small   bit  of   mnscle  com- 

penas  on  tne  size  <  .  tnese  poged  of  four  priniary  fatJCjCUij.  A,  nat- 
fasciculi,  which  may  be  ^S^^.S^S^^ 
readily  seen  in  a  piece  of  maryar 

boiled  beef.  In  good  carving,  meat  is  cut  across  the 
fasciculi,  or  "  across  the  grain,"  as  it  is  then  more  easily 
broken  up  by  the  teeth  ;  the  polygonal  areas  seen  on 
the  surface  of  a  slice  of  beef  are  cross  sections  of  the 
fasciculi.  The  larger  fasciculi  are  subdivided  by  fine 
partitions  of  connective  tissue  into  smaller  (Fig.  32),  each 
consisting  -of  a  few  muscular  fibres  enveloped  in  a  close 

Is  a  muscle  an  organ  or  a  tissue?  What  is  the  chief  tissue  in  it 
called?  What  things  exist  in  it  besides  striped  muscular  tissue?  What 
is  the  use  of  each? 

What  is  the  perirnysium?  How  is  a  muscle  divided  into  fasciculi? 
How  far  do  the  fasciculi  extend?  When  is  meat  coarse  in  texture? 
Why  is  beef  carved  across  the  grain?  Of  what  are  the  fasciculi  com- 
posed? 


THE    HUMAN   BODY. 


network  of  minute  blood-vessels.  "Where  a  muscle  tapers 
the  muscle  fibres  in  the  fasciculi  are  less  numerous  and  when 
a  tendon  is  formed  they  disappear  alto- 
gether, leaving  only  the  connective  tissue. 

Histology  of  Muscle. — The  striped  mus- 
cular tissue,  which  gives  the  muscle  its 
power  of  contracting,  is  found  when  ex- 
amined by  the  microscope  to  be  made  up 
of  extremely  slender  muscular  fibres,  each 
about  one  inch  in  length,  but  most  of 
them  less  than  -^  of  an  inch  across. 

Each  muscular  fibre  has  externally  a 
thin  sheath  or  envelope,  the  sarcolemma, 
which  envelops  the  contracting  part  of  the 
fibre.  This  latter  is  soft  and  almost 


PIG.  33.—  A  small   semi-fluid,  and  under  a  microscope  is  seen 

Siece  of    m«scular 
bre    highly    mag- 
nified.     At  a    the 
fibr«     has    been 
crushed  and  twist- 

ed so  as  to  tear   brighter     transverse      bands      (Fig.     33). 

its  contents,   while  \      o  /• 

aghereiTer;  After  death  tlie  semi-solid  contents  of  the 
to  thele'/t  fibre  solidify  and  death  -stiffening  is  pro- 
6  jfSSSi 

and  conspicuous. 


to    present    a    striped    appearance,    as    if 
made     up     of     alternating     dimmer 


duced 


at   the  same  time   the  fibre  often 

.^     &     immber     Qf     yery     fine 

threads  or  fibrillce,  which  were   formerly  regarded  as  true 
constituents  of  the  living  muscular  fibre. 

Plain  muscular  tissue.  —  The  muscles  hitherto  spoken  of 


Of  what  is  a  tendon  made? 

Of  what  is  striped  muscular  tissue  composed?  Describe  the  form 
and  size  of  muscular  fibres. 

What  is  the  xarcolemmn  ?  What  is  the  consistency  of  the  con- 
tractile part  of  a  living  muscular  fibre?  What  appearance  does  it 
present  under  the  microscope?  What  is  the  cause  of  death  stiffening? 
What  are  fibrillae? 

What  do  we  mean  by  voluDturv  muscles? 


PLAIN   MUSCULAR    TISSUE. 


75 


are  all  more  or  less  under  the  control  of  the  will  ;  we 
can  make  them  contract  or  prevent  this  as  we  choose ; 
they  are  therefore  often  called  the  voluntary  muscles.* 
There  are  in  the  body  other  muscles  whose  contractions 


FIG.  34.— The  muscular  coat  of  the  stomach. 

we  cannot  control,  and  which  are  hence  called  involuntary 
muscles ;  they  are  not  attached  to  the  skeleton  directly, 
nor  concerned  in  our  ordinary  movements,  but  lie  in  the 

"What  by  involuntary?  Which  kind  is  attached  to  the  skeleton? 
Where  do  we  find  the  involuntary  muscles? 

*  No  sharp  line  can  be  drawn  between  voluntary  and  involuntary  muscles ;  the 
muscles  of  respiration  are  to  a  certain  extent  under  the  control  of  the  will  ;  any  one 
can  draw  a  long  breath  when  he  chooses.  But  in  ordinary  quiet  breathing  we  are 
quite  unconscious  of  their  working,  and  even  when  we  pay  heed  to  it  our  control  of 
them  is  limited  ;  no  one  can  hold  his  breath  long  enough  to  suffocate  himself.  In- 
deed, any  one  of  the  striped  muscles  may  be  thrown  into  activity,  independently  of 
or  even  against  the  will,  as  we  see  in  the  "fidgets"  of  nervousness,  and  the  irre- 
pressible trembling  of  extreme  terror.  Functionally,  when  we  call  any  muscle  vol- 
untary, we  mean  that  it  may  be  controlled  by  the  will,  but  not  that  it  necessarily 
always  is  so.  Structurally,  the  heart  occupies  an  intermediate  place  :  its  striped 
fibres  resemble  much  more  those  of  voluntary  than  of  involuntary  muscles,  but  its 
boat  is  not  at  all  subject  to  the  will  ;  though,  as  the  exception  proving  the  rule,  it 
may  he  noted  that  there  is  an  apparently  well-authenticated  case  of  a  person  who 
could  by  an  act  of  will  stop  his  heart. 


76 


THE   HUMAN   BODY. 


walls  of  various  hollow  organs  of  the  body,  as  the  stomach 
(Fig.  34),  the  intestines,  and  the  arteries ;  by  their  con- 
tractions they  move  things  contained  in  those  cavities. 
Like  the  voluntary  muscles,  the  involuntary  consist  of 
contractile  elements,  with  accessory  con- 
nective tissue,  blood-vessels,  and  nerves ; 
but  their  fibres  have  a  very  different  appear- 
ance under  the  microscope.  They  are  not 
cross-striped,  but  are  made  up  of  elongated 
cells  united  by  a  small  amount  of  cement- 
ing material.  Each  cell  (Fig.  35),  is  flat- 
tish,  and  tapers  off  toward  its  ends ;  in  its 
centre  is  a  nucleus  with  one  or  two  nucle- 
oli.  The  cells  have  the  power  of  shortening 
in  the  direction  of  their  long  axes. 

Heart  muscle. — The  muscular  tissue  of 
the  heart  is  not  under  the  control  of  th& 
will ;  it,  however,  is  cross-striped,  and  more 
like  the  voluntary  than  the  ordinary  in- 
voluntary muscle,  though  it  differs  in  some 
FIG.  35.— Unstriped  respects  from  both. 

muscle-cells. 

Speaking  generally,  we  may  say  that 
the  movements  necessary  for  the  nutrition  of  the  body  are 
not  left  for  us  to  look  after  ourselves,  but  are  carried  on 
by  muscles  which  work  involuntarily  ;  the  blood  is 
pumped  round  by  the  heart,  and  food  churned  up  in  the 

What  is  their  function?  What  are  they  composed  of  ?  What  is 
seen  when  a  cell  from  an  involuntary  muscle  is  examined  with  the 
microscope? 

Is  the  heart  muscle  voluntary?  In  what  respect  does  it  resemble 
voluntary  muscle? 

What  movements  of  the  body  does  nature  not  leave  to  our  own 
control?  Give  examples. 


THE   CHEMICAL    COMPOSITION  OF   MUSCLE.        77 

N&(/" 
stomach  and   passed   along  the    intestines,   whetfee*  TT* 

think  about  it  or  not. 

The  chemical  composition  of  muscle. — Muscle  contains 
about  75  per  cent,  of  water ;  and  a  considerable  quantity 
of  salines.  Living,  resting  muscle  is  alkaline  to  test 
paper  ;  hard-worked  or  dying  muscle  is  acid.  Its  chief 
organic  constituents  are  proteid  or  albuminous  substances 
(p.  21),  and  of  these  the  most  abundant  in  a  per- 
fectly fresh  muscle  is  rtutt&n.  Soon  after  death  the 
myosin  clots.  Dilute  acids  dissolve  myosin  and  turn  it 
into  syntonin,  which  used  to  be  thought  the  chief  pro- 
teid of  muscle. 

Beef  tea. — When  lean  meat  is  heated  its  myosin  is 
converted  into  a  solid  insoluble  substance  much  like  the 
white  of  a  hard-boiled  egg.  Hence,  when  a  muscle  is 
boiled  most  of  its  proteid  is  coagulated  and  stays  in  the 
meat  instead  of  passing  out  into  the  soup.  Even  if  beef 
be  soaked  first  in  cold  water  this  is  still  the  case,  as  myo- 
sin is  not  soluble  in  water.*  It  follows  that  beef  tea  as 
ordinarily  made  contains  little  but  the  flavoring  matters  and 
salts  of  the  beef,  and  some  gelatin  dissolved  out  from  the 
connective  tissue  of  the  muscle.  The  flavoring  matters 

What  proportion  of  water  does  muscle  contain?  What  other  in- 
organic compounds  do  we  rind  in  it?  What  is  the  reaction  of  living 
muscle?  How  is  this  changed  by  work  or  death?  What  are  its  main 
organic  constituents?  Name  the  most  abundant  of  these?  What 
change  occurs  in  it  after  death?  What  is  syntonin? 

What  happens  to  the  myosin  when  muscle  is  heated?  When  we 
boil  meat  does  its  myosin  become  dissolved  in  the  soup?  Can  we  get 
the  myosin  out  of  beef  by  soaking  it  in  cold  water?  What  things  are 
found  in  ordinary  beef  tea? 

*  To  get  over  this  difficulty,  various  methods  of  making  beef  tea  have  been  sug- 
gested, in  which  the  chopped  meat  is  soaked  an  hour  or  two  in  strong  brine  or  in 
very  dilute  muriatic  acid.  In  these  ways  the  myosdn  can  be  dissolved  out  of  the 
beef  ;  but  the  product  has  such  an  unoleasant  taste  that  no  one  is  likely  to  swallow 
it,  and  least  of  all  a  eick  person 


78  THE    HUMAN   BODY. 

make  it  deceptively  taste  as  if  it  were  a  strong  solution  of 
the  whole  meat,  whereas,  it  contains  but  a  small  propor- 
tion of  the  really  nutritious  parts,  which  are  chiefly  left 
behind  in  tasteless  shrunken  shreds,  when  the  liquor  is 
poured  off.  Some  things  dissolved  out  of  the  meat  make 
beef  tea  a  slight  stimulant,  but  its  really  nutritive  value 
is  small,  and  it  cannot  be  relied  upon  to  keep  up  a  sick 
person's  strength  for  any  length  of  time. 

Liebig's  extract  of  meat  is  essentially  but  a  concentrated 
beef  tea;  from  its  stimulating  effect  it  is  often  useful  to 
persons  in  feeble  health,  but  other  food  should  be  given 
with  it.  It  contains  all  the  flavoring  matters  of  the  meat, 
and  its  proper  use  is  for  making  gravies  and  flavoring 
soups  ;  the  erroneousness  of  the  common  belief  that  it  is 
a  highly  nutritious  food  cannot  be  too  strongly  in- 
sisted upon,  as  sick  persons  may  be  starved  on  it  if  igno- 
rantly  used. 

Various  meat  extracts  are  now  prepared  by  subjecting 
beef  to  chemical  processes  in  which  it  undergoes  changes 
like  those  experienced  in  digestion.  The  myosin  is  thus 
made  soluble  in  water  and  uncoagulable  by  heat,  and  a  real 
concentrated  meat  extract  is  obtained.  Before  relying  on 
any  one  of  them  for  the  feeding  of  an  invalid,  it  would, 
however,  be  well  to  insist  or.  having  a  statement  of  its 


"Why  does  beef  tea  taste  as  if  all  the"  strength  "  of  the  meat  were  in 
it?  Where  do  the  chief  nutritious  parts  remain  when  beef  tea  is 
strained  off  the  meat?  What  is  the  action  of  beef  tea  on  the  system? 

What  is  Liebig's  extract  of  meat  ?  Why  is  it  sometimes  useful  to 
invalids  ?  What  should  be  given  them  in  addition  ?  What  is  its 
proper  use  ?  Why  is  it  important  to  know  thai  it  is  not  a  nutritious 
food? 

How  are  some  other  meat  extracts  made?  How  is  the  myosin 
changed  in  preparing  them  ?  Are  they  all  to  be  relied  on  indiscrimi 
nately?  What  should  be  done  before  trusting  the  nutrition  of  a 
feeble  person  to  any  one  of  them? 


MEAT   EXTRACTS.  79 

method  of  preparation,  and  then  to  consult  a  physician,  or 
some  one  else  who  has  the  requisite  knowledge,  in  order  to 
ascertain  if  the  method  is  such  as  might  be  expected  to 
really  attain  the  end  desired. 


CHAPTER  VII. 
MOTION  AND  LOCOMOTION. 

The  special  physiology  of  muscles. — The  distinctive  prop- 
erties of  muscle  are  everywhere  the  same  ;  it  has  the  power 
of  contracting ;  but  the  uses  of  different  muscles  are  very 
varied  by  reason  of  the  different  parts  to  which  they  are 
attached.  Some  are  muscles  of  respiration,  others  of 
siv allowing  ;  some  bend  joints  and  are  called  flexors,  others 
straighten  them  and  are  called  extensors,  and  so  on. 
The  determination  of  the  exact  use  of  any  particular 
muscle  is  known  as  its  special  physiology,  as  distinguished 
from  its  general  physiology,  or  properties  as  a  muscle, 
without  reference  to  its  use  as  a  muscle  in  a  particular 
place.  We  may  here  consider  the  special  physiology  of  the 
muscles  concerned  in  standing  and  walking. 

Levers  in  the  body. — In  nearly  all  cases  the  voluntary 
muscles  carry  out  their  special  functions  with  the  co-oper- 
ation of  the  skeleton  ;  most  of  them  are  joined  to  bones 
at  each  end  and  when  they  contract  move  the  bones, 

In  what  respect  are  all  muscles  alike?  Have  all  muscles  the  same 
uses?  Give  instances  of  the  employment  of  muscles  for  different  pur- 
poses. What  is  meant  by  the  special  physiology  of  a  muscle?  What 
by  its  general  physiology? 

With  what  do  the  voluntary  muscles  co-operate?  To  what  are  the 
ends  of  nearly  all  muscles  attached?  What  happens  when  a  muscle 
contracts? 

[80] 


THE    DIFFERENT    KINDS    OF   LEVERS.  81 

and,  secondarily,  the  soft  parts  attached  to  these.  When 
muscles  move  bones  the  latter  are  almost  invariably  to  be 
regarded  as  levers  whose  fulcra  lie  at  the  joint  where  the 
movement  takes  place.  Examples  of  the  three  forms  of 
levers  recognized  in  mechanics  are  found  in  the  human 
body. 

Levers  of  the  first  order.— In  this  form  (Fig.  36),  the 
fulcrum  or  fixed  supporting  point,  F,  lies  between  the 
weight  to  be  moved  and  the  moving  power.  The  distance 


i 


FIG.  36.— A  lever  of  the  first  order.    F,  fulcrum  ;  P,  power  ;  W,  resistance  or 
weight. 

PF  from  the  power  to  the  fulcrum  is  called  the  power- 
arm  of  the  lever,  and  the  distance  WF  is  the  weight- 
arm.  When  power-arm  and  weight-arm  are  equal  (as  in 
an  ordinary  pair  of  scales),  no  mechanical  advantage  is 
gained  ;  to  lift  a  pound  at  W,  P  must  be  pressed  down 
with  a  force  greater  than  a  pound  ;  and  the  end  W  will 
go  up  just  as  far  as  the  end  P  goes  down.  If  PF  be 
longer  than  WF  then  a  small  weight  at  P  will  balance  a 
larger  one  at  W,  the  gain  being  greater  the  greater  the 
difference  in  the  length  of  the  arms,  but  the  distance 
through  which  W  is  moved  will  be  less  than  that 
through  which  P  moves  ;  for  example,  if  PF  be  twice  as 

How  are  the  bones  moved  by  muscles  to  be  regarded?  Where 
do  the  fulcra  of  these  levers  lie?  How  many  kinds  of  levers  are 
found  in  the  body? 

Describe  a  lever  of  the  first  order.  Define  power-arm  and  weight- 
arm.  When  is  a  mechanical  advantage  gained  by  such  a  lever? 


82  THE   HUMAN   BODY. 

long  as  WF  then  half  a  pound  at  P  would  balance 
against  a  pound  at  W,  and  just  over  half  a  pound  laid  on 
the  end  P  would  lift  a  pound  on  the  end  W,  but  W  would 
only  go  up  half  as  far  as  P  went  down.  On  the  other 
hand,  if  the  weight-arm  were  longer  than  the  power-arm 
there  would  be  a  loss  in  force,  but  a  gain  in  the  distance 
through  which  the  weight  was  moved. 

Examples  of  levers  of  the  first  order  are  not  numer- 
ous in  the  human  body.  One  is  found  in  nodding 
movements  of  the  head,  the  fulcrum  being  where  the 
occipital  bone  articulates  with  the  atlas  (Fig.  20).  When 
the  chin  is  raised  the  power  is  applied  to  the  skull  behind 
the  fulcrum  by  muscles  passing  from  the  spinal  column 


W 


FIG.  37.— A  lever  of  the  second  order.    P.  f  nlcrnm ;   P,  power ;    W,  weight. 
The  arrows  indicate  the  direction  in  which  the  forces  act. 

to  the  back  of  the  head  ;  the  resistance  to  be  overcome  is 
the  excess  in  weight  of  the  part  of  the  head  in  front  of 
the  fulcrum  over  that  behind  it,  and  is  not  great,  as  the 
head  is  nearly  balanced  on  the  top  of  the  spine.  To  let 
the  chin  drop  does  not  necessitate  any  muscular  effort. 

Levers  of  the  second  order. — In  this  form  of  lever 
(Fig.  37),  the  weight  or  resistance  acts  between  the  ful- 
crum and  the  power.  The  power-arm  PF  is  accordingly 

What  is  lost  when  power  is  gained? 

Are  there  many  levers  of  the  first  order  in  the  body?    Give  an 
sample  of  one,  describing  the  action. 
Describe  a  lever  of  the  second  order. 


LEVERS  IN  THE  BODY.  83 

always  longer  than  the  weight-arm,  WF,  and  so  a  com- 
paratively weak  force  can  overcome  a  considerable  resist- 
ance. There  is,  however,  a  loss  in  rapidity  and  extent  of 
movement,  since  it  is  obvious  that  when  P  is  raised  a 
certain  distance  W  will  be  raised  less.  As  an  example  of 
this  kind  of  lever  we  may  take  the  act  of  standing  on 
the  toes.  Here  the  foot  is  the  lever,  and  the  fulcrum  is 
where  its  fore  part  rests  on  the  ground  ;  the  weight  is 
that  of  the  body,  and  acts  downwards  through  the  ankle 
ioint  at  Ta,  Fig.  19  ;  the  power  is  the  great  muscle  of  the 
calf  of  the  leg  pulling  by  its  tendon,  which  is  fixed  to  the 
end  of  .the  heel  bone,  Ca. 

Levers  of  the  third  order. — In  these  (Fig.  38),  the 
power  is  applied  between  the  fulcrum  and  the  weight ; 
hence  the  power-arm  PF,  is  always  shorter  than  the 


W 


FIG.  88.— A  lever  of  the  third  order.    F,  fulcrum  ;  P,  power  ;  TP,  weight. 


weight-arm,  WF.  The  moving  force  acts  at  a  mechani- 
cal disadvantage,  but  swiftness  and  range  of  movement 
are  gained  ;  this  is  the  form  of  lever  most  commonly  used 
in  the  body.  For  example,  when  the  forearm  is  bent  up 
towards  the  arm  the  fulcrum  is  the  elbow  joint  (Fig.  29) ; 

What  is  the  mechanical  gain  in  such  levers?  What  is  the  loss? 
Give  an  example  of  employment  of  a  lever  of  the  second  order  in 
the  body,  poiuting  out  fulcrum,  point  of  action  of  the  weight,  and 
point  of  application  of  t!:e  power. 

Describe  a  lever  of  the  third  order.  What  is  lost  and  what 
gained  by  it?  Is  it  often  used  in  the  body?  Give  an  example 


84  THE   HUMAN  BODY 

the  power  is  applied  at  the  insertion  of  the  biceps  muscle 
into  the  radius ;  the  weight  is  that  of  the  forearm  and 
hand  and  whatever  may  be  held  in  the  latter,  and  acts  at 
the  centre  of  gravity  of  the  whole,  somewhere  on  the  far 
side  of  the  point  of  application  of  the  power.  Usually 
(as  in  this  case),  the  power-arm  is  very  short,  so  as  to  gain 
speed  and  extent  of  movement,  the  muscles  being  strong 
enough  to  work  at  a  considerable  mechanical  disadvantage. 
The  limbs  are  thus  also  made  much  more  shapely  than 
would  be  the  case  were  the  power  applied  near  or  beyond 
the  weight. 

Pulleys  in  the  body, — Fixed  pulleys  are  used  in  the 
body  ;  they  give  rise  to  no  loss  or  gain  of  power,  but 
serve  to  change  the  direction  in  which  certain  muscles 
pull.  One  of  the  muscles  of  the  eye- ball,  for  example, 
has  its  origin  at  the  back  of  the  eye-socket,  from 
there  it  passes  to  the  front  and  ends,  before  it  reaches  the 
eye-ball,  in  a  long  tendon.  This  tendon  passes  on  to  the 
margin  of  the  frontal  bone,  which  arches  over  the  front 
of  the  eye-socket,  and  there  passes  through  a  ring 
and  turns  back  to  the  eye-ball.  The  direction  in  which 
the  muscle  moves  the  eye  is  thus  quite  different  from 
what  it  would  be  if  the  tendon  went  directly  to  the  eye- 
ball. 

Standing. — We  only  slowly  learn  to  stand  in  the  year 
or  two  after  birth,  and  though  we  finally  come  to  do  it 
without  conscious  attention,  standing  always  requires  the 
co-operation  of  many  muscles,  guided  and  controlled  by 

Why  is  the  power-arm  in  the  body  usually  short? 
What  kind  of  pulley  is  used  in  the  body?    Is  any  mechanical  ad 
vantage  gained  from  it?    What  is  it  used  for?    Give  an  example. 
Is  standing  a  simple  process? 


STANDING.  85 

the  nervous  system.  The  influence  of  the  latter  is  shown 
by  the  fall  which  follows  a  severe  blow  on  the  head,  which 
has  fractured  no  bone  and  injured  no  muscle  ;  "  the  con- 
cussion of  the  brain"  stuns  the  man,  and  until  it  has 
passed  off  he  cannot  stand. 

When  we  stand  erect,  with  the  arms  close  by  the  sides 
and  the  feet  together,  the  centre  of  gravity  of  the  whole 
adult  body  lies  at  the  articulation  between  the  sacrum 
and  the  last  lumbar  vertebra,  and  a  perpendicular 
drawn  from  it  will  reach  the  ground  between  the  feet. 
In  any  position  in  which  this  perpendicular  falls  within 
the  space  bounded  by  a  line  drawn  close  around  both  feet, 
we  can  stand.  When  the  feet  are  together  the  area  enclosed 
by  this  line  is  small,  and  a  slight  sway  of  the  trunk 
would  throw  a  perpendicular  dropped  from  the  centre  of 
gravity  of  the  body  outside  it  ;  the  more  one  foot  is  in 
front  of  the  other  the  greater  the  sway  back  or  forward 
which  will  be  compatible  with  safety,  and  the  greater  the 
lateral  distance  between  the  feet  the  greater  the  lateral 
sway  which  is  possible  without  falling.  Consequently, 
when  a  man  wants  to  stand  very  firmly  he  advances  one 
foot  obliquely,  so  as  to  increase  his  base  of  support  both 
from  before  back,  and  from  side  to  side. 

In  consequence  of  the  flexibility  of  its  joints  a  dead 
body  cannot  be  balanced  on  its  feet  as  a  statue  can. 
When  we  stand,  the  ankle,  knee,  and  hip-joints,  if  not 
braced  by  the  muscles,  would  give  way,  and  the  head  also 

Illustrate  the  influence  of  the  nervous  system  in  connection  with 
'standing. 

Where  is  the  centre  of  gravity  of  the  body  when  we  stand  erect? 
Where  does  a  perpendicular  from  it  reach  the  ground?  Why  do  we 
separate  the  feet  when  we  want  to  stand  firmly? 

Why  cannot  a  dead  body  be  balanced  on  its  feet?  What  prevents 
our  knee,  and  hip-joints  from  bending  when  we  stand? 


86 


THE    HUMAN   BODY. 


(f 

1  ^ 


fall  forward  on  the  chest.  But  (Fig.  39)  muscles,  1,  in 
front  of  the  ankle-joint,  and  others,  I,  behind  it,  both 
contracting  at  the  same  time,  keep  the 
joint  from  yielding  ;  similarly  muscles 
(2)  in  front  of  the  knee  and  hip-joints 
are  opposed  by  others  (II)  behind 
them,  and  when  we  stand  both  con- 
tract to  a  certain  extent  and  keep  those 
joints  rigid  ;  and  the  muscles  (III), 
which  run  from  the  pelvis  to  the  back 
of  the  head  similarly  pull  against 
others,  3  and  4,  which  run  from  the 
pelvis  to  the  lower  end  of  the  breast- 
bone, and  from  the  upper  end  of  the 
breastbone  to  the  anterior  part  of  the 
skull,  and  their  balanced  contraction 
keeps  the  head  erect.  Since  the  degree 
to  which  each  muscle  concerned  con- 
tracts when  we  stand  must  be  accu- 
rately adjusted  to  the  contraction  of 
its  antagonist  on  the  opposite  side  of 
the  joint,  we  may  easily  comprehend 
why  it  takes  us  some  time  to  learn  to 
stand,  and  why  a  stunned  man,  whose 
muscles  have  lost  guidance  from  the 
nervous  system,  falls. 

Locomotion  includes  all  movements 
i  of  the  body  in  space,  dependent  on 

its    own    unaided     muscular    efforts, 
such  as  walking,  running,  leaping,  and  swimming. 

Explain  how  the  different  joints  concerned  are  "  braced  "  in  stand 
ing.     Why  does  it  take  a  child  some  time  to  learn  to  stand? 
What  is  meant  in  physiology  by  locomotion? 


| 


SfjotS?  «d*bj 


WALKING.  8? 

Walking. — In  walking,  the  body  never  entirely  quits 
the  ground,  the  heel  of  the  advanced  foot  reaching  this 
before  the  toe  of  the  rear  foot  has  been  raised  from  it.  In 
each  step  the  advanced  leg  supports  the  body,  and  the 
foot  behind  at  the  beginning  of  the  step  propels  it. 

A  little  attention  will  enable  any  one  to  analyze  the 
act  of  walking  for  himself.  Stand  with  the  heels  to- 
gether and  take  a  step,  commencing  with  the  left  foot.  The 
whole  body  is  at  first  inclined  forwards,  the  movement 
taking  place  mainly  at  the  ankle  joints.  This  throws  the 
centre  of  gravity  in  front  of  the  base  formed  by  the 
feet,  and  a  fall  would  result  were  not  the  left  foot  simul- 
taneously raised  by  bending  the  knee  a  little,  and  swung 
forwards,  the  toes  just  clear  of  the  ground  and  the  sole 
nearly  parallel  to  it.  When  the  step  is  completed  the  left 
knee  is  straightened  and  the  foot  placed  on  the  ground, 
the  heel  touching  first ;  the  base  is  thus  extended  in  the 
direction  of  the  stride  and  the  fall  prevented.  Meanwhile 
the  right  leg  is  kept  straight  but  inclined  forwards,  carry- 
ing the  trunk  during  the  step  while  the  left  foot  is  off  the 
ground ;  at  the  same  time  the  right  foot  is  raised,  com- 
mencing with  the  heel ;  when  the  step  of  the  left  leg  is 
completed  only  the  great  toe  of  the  right  is  in  contact 
with  the  support.  With  this  toe  a  push  is  given  which 
sends  the  body  swinging  forward,  supported  on  the  left 
leg,  which  now  in  turn  is  kept  rigid  except  at  the  ankle 
joint ;  the  right  knee  is  immediately  afterwards  bent  and 
that  leg  swings  forwards,  its  foot  just  clear  of  the  ground, 
as  the  left  did  before.  The  body  meanwhile  is  supported 

Is  the  body  ever  off  the  ground  in  walking?     Describe  the  act  of 

walking. 


88  THE    HUMAN   BODY. 

on  the  left  leg  alone.  When  the  right  leg  completes  its  step 
its  knee  is  straightened  and  the  foot  thus  brought,  heel 
first,  on  the  ground  ;  while  it  is  swinging  forwards  the  left 
foot  is  gradually  raised,  and  at  the  end  of  the  step  its  great 
toe  alone  is  on  the  ground  ;  with  this  a  push  is  given  as 
before  with  that  of  the  right  foot,  and  the  left  leg  then 
swings  forward  to  make  the  next  step.  Walking  may,  in 
fact,  be  briefly  described  as  the  act  of  continually  falling 
forwards  and  preventing  the  completion  of  the  fall  by 
thrusting  out  a  leg  to  meet  the  ground  in  front. 

During  each  step  the  body  sways  a  little  from  side  to 
side,  as  it  is  alternately  borne  by  the  right  and  left  legs. 
It  also  sways  up  and  down  a  little  ;  a  man  standing  with 
his  heels  together  is  taller  than  when  one  foot  is  advanced, 
just  as  a  pair  of  compasses  held  erect  on  its  points  is  high- 
er when  its  legs  are  together  than  when  they  straddled 
apart ;  in  that  period  of  each  step  when  the  advancing 
trunk  is  balanced  vertically  over  one  leg,  the  walker's  trunk 
is  more  elevated  than  when  the  front  foot  also  is  on  the 
ground.  Women,  accordingly,  often  find  that  a  dress 
which  clears  the  ground  when  they  are  standing  sweeps 
the  pavement  when  they  walk. 

The  length  of  each  step  is  primarily  dependent  on  the 
length  of  the  legs,  though  it  can  be  largely  controlled  by 
special  muscular  effort,  as  we  see  in  a  regiment  of  soldiers. 
all  of  whom  have  been  taught  to  take  the  same  stride,  no 
matter  how  their  legs  vary  in  length.  In  natural  easy 
walking,  little  muscular  effort  is  employed  to  carry  the 
rear  leg  forward  after  it  has  given  its  push  ;  it  swings  on 

At  what  part  of  a  step  is  a  man  tallest?    Give  illustrations. 
What  primarily  determines  the  lengti  Df  a  person  s  step?    Can 
this  length  be  controlled? 


U7G113NE    OF    THE    MUSCLES.  89 

like  a   pendulum  once  its  foot  is  raised  from  the  ground. 

IAs  short  pendulums  swing  faster  than  long  ones  the  natu- 
ral step  of  short-legged  people  is  quicker  than  that  of 
long-legged. 

Running  differs  from  walking  in  several  respects. 
There  is  a  moment  when  both  feet  are  off  the  ground  ; 
the  toes  alone  come  in  contact  with  it  at  each  step  ;  and 
the  knee  joint  is  not  straight  at  the  end  of  the  step.  In 
running,  when  the  rear  foot  is  to  leave  the  ground  the 
knee  is  suddenly  straightened,  and  the  ankle-joint  extend- 
ed so  as  to  push  the  toes  forcibly  on  the  support  and  pow- 
erfully impel  the  whole  body  forwards  and  upwards.  The 
knee  is  then  considerably  flexed  and  the  foot  raised  some 
way  from  the  ground,  and  this  occurs  before  the  toes  of  the 
front  foot  reach  the  support.  The  raised  leg  in  each  step  is 
forcibly  drawn  forward  by  its  muscles  and  not  allowed  to 
swing  passively  as  in  quiet  walking.  This  increases  the 
rate  at  which  the  steps  follow  one  another,  and  the  stride 
is  increased  by  the  sort  of  one-legged  jump  that  occurs 
through  the  jerk  given  by  the  straightening  knee  of  the 
rear  leg,  just  before  it  leaves  the  ground. 

Hygiene  of  the  Muscles. — The  healthy  working  of  the 
muscles  is  dependent  on  a  healthy  state  of  the  body  in 
general ;  this  is  indispensable  that  they  may  be  sufficiently 
supplied  with  proper  nourishment,  and  have  their  wastes 
promptly  carried  away.  Hence  good  food  and  pure  air  are 
necessary  for  a  vigorous  muscular  system.  Muscles  also 

"Why  do  short  legged  persons  tend  to  take  a  quicker  step  than 
others? 

How  does  running  differ  from  walking?  Describe  the  act  of  run- 
ning. How  is  the  number  of  steps  taken  in  a  given  time  increased  in 
running?  How  is  the  stride  increased? 

How  does  the  state  of  general  health  influence  the  muscular  sys- 
tem? Why  does  an  athlete  need  good  food  and  air? 


90  THE    HUMAN   BODY. 

should  not  he  exposed  to  any  considerable  continued 
pressure,  since  this  interferes  with  the  flow  of  blood 
and  lymph  through  them  which  is  essential  for  their  nu- 
trition. 

Exercise  is  necessary  for  the  best  development  of  the 
muscles.  A  muscle  long  left  unused  diminishes  in  bulk 
and  degenerates  in  quality,  as  is  well  seen  when  a  muscle  is 
paralyzed  and  remains  permanently  inactive  because  of 
disease  of  its  nerve  ;  although  at  first  the  muscle  itself 
may  be  perfectly  healthy,  it  alters  in  a  few  weeks,  and 
when  the  nerve  is  repaired  the  muscle  may  in  turn  be  in- 
capable of  activity.  The  same  fact  is  illustrated  by  the 
feeble  and  wasted  state  of  the  muscles  of  a  limb  which 
has  been  kept  motionless  in  splints  for  a  long  time  :  when 
the  splints  are  removed  it  is  only  after  careful  and  per- 
sistent exercise  that  the  long  idle  muscles  regain  their 
former  size  and  power.  The  great  muscles  of  the 
"brawny  arm"  of  the  blacksmith  illustrate  the  converse 
fact — the  growth  of  muscles  when  exercised. 

Exercise,  to  be  useful,  must  be  judicious ;  taken  to 
the  point  of  extreme  fatigue,  day  after  day,  it  does  harm. 
When  a  muscle  is  worked  its  substance  is  used  up  ;  at 
the  same  time  and  afterwards  more  blood  flows  to  it, 
and  if  the  exercise  is  not  too  violent  and  the  intervals  of 
rest  are  long  enough,  the  repair  and  growth  will  keep  pace 
with  or  exceed  the  wasting  :  but  excessive  work  and  too 
short  rest  will  lead  to  diminution  and  enfeeblenient  of  the 
muscle  ju-st  as  certainly  as  too  little  exercise. 

Few  persons  can  profitably  attempt  to  work  hard  daily 

Why  should  muscles  not  be  exposed  to  continuous  pressure? 

What  happens  when  a  muscle  is  not  used?  Illustrate  by  examples. 
Why  are  the  muscles  of  a  blacksmith's  arm  large? 

When  doet  exercise  do  harm?  Why?  Can  most  persons  work 
hard  with  both  brain  and  muscle  at  the  same  time? 


VARIETIES  OF  EXERCISE.  91 

with,  both  brain  and  muscle,  but  all  should  regularly  use 
both ;  choosing  which  to  work  with,  and  which  to  simply 
exercise.  The  best  earthly  life,  that  of  the  healthy  mind  in 
the  healthy  body,  can  only  so  be  attained.  For  persons  of 
average  physique,  engaged  in  study  or  business  pursuits  of 
a  sedentary  nature,  the  minimum  of  daily  exercise  should 
be  an  amount  equivalent  toaTfive^mile  walk. 

Time  for  Exercise. — Since  extra  muscular  work  means 
extra  muscular  waste,  and  should  be  accompanied  by  an 
abundant  supply  of  food  materials  to  the  muscles,  violent 
exercise  should  not  be  taken  after  a  long  fast.  Neither 
should  it  be  taken  immediately  after  a  meal ;  a  great  deal 
of  blood  is  then  needed  in  the  digestive  organs  to  provide 
materials  for  digesting  the  food,  and  this  blood  cannot  be 
sent  off  to  the  muscles  without  the  risk  of  an  attack  of 
indigestion.  Strong  and  hearty  young  people  may  take  a 
long  walk  before  breakfast,  but  others  had  better  wait  un- 
til after  eating  something  before  engaging  in  any  kind  of 
hard  work. 

Varieties  of  Exercise. — In  walking  and  running  the 
muscles  chiefly  employed  are  those  of  the  lower  limbs  and 
trunk  ;  these  exercises  leave  the  muscles  of  the  chest  and 
arms  imperfectly  worked.  Rowing  is  better,  since  in 
it  nearly  all  the  muscles  are  used.  No  one  exercise  em- 
ploys in  proper  proportion  all  the  muscles,  and  gymnasia 
in  which  different  feats  of  agility  are  practiced  so  as  to 
call  different  muscles  into  action  have  a  deserved  popu- 


How  can  the  highest  development  of  man,  regarded  merely  as  a 
thinking  and  moving  machine,  be  attained? 

Why  should  we  not  exercise  when  fasting?  Why  not  soon  after 
eating? 

What  muscles  are  chiefly  used  in  walking  and  running?  Wliich 
are  imperfectly  exercised?  Why  are  gymnasia  useful? 


92  THE   HUMAN   BODY. 

iarity.  It  should  be  borne  in  mind,  however,  that  the 
legs  especially  need  strength  ;  while  in  the  arms  delicacy 
of  movement  is  more  important  to  most  persons  than 
great  strength ;  and  the  fact  that  gymnastics  are  usually 
practiced  indoors  is  also  a  great  drawback  to  their  value. 
Out  of  door  exercise  in  good  weather  is  better  than  any 
other,  and  every  one  can  at  least  take  a  walk.  The  daily 
" constitutional"  is  very  apt  to  become  wearisome,  es- 
pecially to  young  persons,  and  exercise  loses  half  its  value 
if  unattended  with  feelings  of  mental  relaxation  and  pleas- 
ure. Active  games,  for  this  reason,  have  a  great  value  for 
young  and  healthy  persons  ;  lawn  tennis,  base  ball,  and 
cricket  are  all  attended  with  pleasurable  excitement,  and 
are  excellent  also  as  exercising  many  muscles. 

What  is  chiefly  needed  in  the  muscles  of  arms  and  legs  respect- 
ively? Point  out  conditions  under  which  muscular  exercise  loses 
much  of  its  value.  Why  are  athletic  games  especially  useful? 


CHAPTER  VIII. 
WHY   WE  EAT    AND    BREATHE. 

How  is  it  that  the  body  can  do  muscular  work  ? — In  the 

muscles  we  possess  a  set  of  organs  capable  of  moving  the 
body  from  place  to  place,  of  changing  the  relative  positions 
of  its  parts,  and  of  lifting  external  objects  :  as  long  as  we 
are  alive,  more  or  fewer  of  our  muscles  are  every  moment 
doing  some  mechanical  work.  This  fact  suggests  the 
question,  where  does  this  power  of  working  come  from  ? 
In  a  few  words,  the  answer  is,  it  comes  from  the  burning 
of  parts  of  the  body  itself  :  in  the  burning,  work-power  or 
energy  is  set  free  and  some  of  this  is  used  by  the  muscles. 
The  conservation  of  energy. — The  different  natural 
forces  known  to  us  are  not  nearly  so  numerous  as  the 
kinds  of  matter  :  we  all,  however,  know  several  of  them, 
as  light,  heat,  electricity,  and  mechanical  work.  One  of 
the  greatest  discoveries  of  the  nineteenth  century  is  that 
these  different  natural  forces,  or  forms  of  energy,  can  be 
turned  one  into  another,  directly  or  indirectly :  kinds  of 
energy  are  transmutable,  while,  so  far  as  we  know  at  pres- 

What  are  the  functions  of  the  muscles?  Are  all  of  our  muscles  ever 
at  rest  at  the  same  time  ? 

What  question  does  the  constant  activity  of  our  muscles  suggest? 
How  may  this  question  be  briefly  answered  ? 

Name  some  forms  of  energy.  Can  they  be  turned  from  one 
form  to  another  ? 


94  THB    HUMAN   BODY. 

ent,  kinds  of  matter  are  not.  We  cannot,  as  the  alchemists 
hoped,  turn  iron  or  mercury  into  gold,  but  we  can  turn 
light  into  heat,  and  heat  into  electrical  force,  or  into  me- 
chanical work.  When  such  transformations  are  made  it  is 
always  found  that  a  definite  amount  of  one  kind  of  energy 
disappears  to  give  rise  to  a  certain  definite  amount  of  an- 
other. In  other  words,  it  has  been  discovered  that  energy 
cannot  be  created :  if  we  take  a  given  quantity  of  heat  we 
can  turn  some  of  it  into  mechanical  work  ;  if  we  then, 
turn  all  this  mechanical  work  back  into  heat  we  get 
again  exactly  the  quantity  of  heat  which  disappeared 
when  the  mechanical  work  appeared  :  and  so  with  all  other 
transformations  of  energy  from  one  kind  to  another,  and 
back  again.  This  fact  that  energy  or  work-poiver  can  be 
turned  from  one  kind  into  another,  and  often  lack  again, 
but  never  created  from  nothing  or  finally  destroyed)  is 
known  as  the  law  of  the  conservation  of  energy. 

Illustrations  of  the  conservation  of  energy. — In  a  steam- 
engine,  heat,  which  is  the  best  known  kind  of  energy,  is 
produced  in  the  furnace  ;  when  the  engine  is  at  work  all 
of  this  energy  does  not  leave  it  as  heat ;  some  is  turned  into 
mechanical  work,  and  the  more  work  the  engine  does  the 
greater  is  the  difference  between  the  heat  generated  in  the 
furnace  and  that  leaving  the  machine.  If,  however,  we 
used  the  work  to  rub  two  rough  surfaces  together  we 
could  get  the  heat  back,  and  if  (which  of  course  is  im- 
possible in  practice)  we  could  avoid  all  friction  between 

Can  matter  be  transmuted  ?  What  is  always  found  when  energy 
is  transformed  ? 

Can  man  create  energy  ?  Illustrate  the  fact  that  energy  can  be 
changed  in  kind  but  not  created.  What  is  meant  by  the  law  of  the 
conservation  of  energy  ? 

Give  an  illustration  of  the  conservation  of  energy. 


TEE    CONSERVATION    OF   ENERGY.  95 

the  moving  parts  of  the  machine,  and  have  all  parts  of  .the 
engine  at  the  end  of  the  experiment  exactly  at  the  same 
temperature  as  at  its  beginning,  the  quantity  of  heat  thus 
obtained  would  be  exactly  equal  to  the  difference  between 
that  amount  of  heat  originally  generated  in  the  furnace 
of  the  engine,  and  the  quantity  which  had  been  carried  off 
from  it  to  tiie  air  since  its  fire  was  lighted.  Having 
turned  some  of  the  heat  into  mechanical  work  we  could 
thus  turn  the  work  back  into  heat  again,  and  find  it  yield 
exactly  the  amount  which  seemed  lost. 

Or  we  might  use  the  engine  to  drive  an  electro-magnetic 
machine  and  so  turn  part  of  the  heat  liberated  in  its  fur- 
nace, first  into  mechanical  work,  and  this  afterwards  into 
electricity;  and  if  we  chose  to  use  the  latter  with  the  proper 
apparatus,  as  now  used  for  electric  lighting,  we  could  turn 
more  or  less  of  it  into  light;  and  so  have  a  great  part  of  the 
energy  which  first  became  conspicuous  as  heat  in  the  engine 
furnace,  now  manifested  in  the  form  of  light  at  some  dis- 
tant point.  In  fact,  starting  with  a  given  quantity  of  one 
kind  of  energy,  we  may  by  proper  contrivances  turn  all 
or  some  of  it  into  one  or  more  other  forms  ;  but  if  we  col- 
lected all  the  final  forms  and  retransformed  them  into  the 
first,  we  should  have  exactly  the  amount  of  it  which  had 
disappeared  when  the  other  kinds  appeared. 

Why  we  need  food. — Energy,  as  we  have  seen,  cannot  be 
created  from  nothing ;  since  the  body  constantly  expends 
energy,  it  must  have  a  steady  supply.  This  supply  comes 

Give  an  example  of  the  transformation  of  heat  into  electrical 
force.  Of  electrical  force  into  light.  Given  a  supply  of  one  kind  of 
energy  what  can  we  do  with  it?  What  would  we  find  if  we  collected 
all  the  final  manifestations  of  energy  and  turned  them  back  into  the 
original  form  ? 

Why  mast  the  body  have  a  steady  supply  of  energy  ?  Where 
ioes  the  supply  come  from  ? 


96  THE  HUMAN  BODY. 

from  the  energy  liberated  when  parts  of  the  body  are  burned, 
or,  as  the  chemists  say,  oxidized,  just  as  that  used  by  a 
locomotive  comes  from  the  burning  or  oxidation  of  coal  or 
wood  in  its  furnace.  In  consequence  of  this  constant  oxi- 
dation, which  destroys  the  tissues  of  the  body  as  coal  is 
destroyed  in  a  furnace,  new  materials  must  constantly  be 
supplied  to  make  up  for  those  used  for  oxidation.  These 
new  materials  are  provided  in  our  food.  One  chief  reason 
of  our  needing  to  eat,  is  that  we  may  replace  the  parts  of 
the  body  which  have  been  burned  in  order  to  set  free  the 
energy  which  we  spend  in  our  muscular  movements. 

Why  the  body  is  warm. — As  a  working  steam-engine  is 
1  warm  so  are  our  bodies,  because  all  the  energy  which  is  set 
free  when  substances  are  burned  in  them,  is  not  turned 
into  mechanical  work,  but  some  of  it  appears  as  heat. 
This  keeping  warm  is  a  very  important  matter,  for  experi- 
ment shows  that  no  tissue  of  the  human  body  works  well 
when  cooled  down  even  a  few  degrees  below  98.5°  F., 
which  is  its  natural  healthy  temperature.  Careful  experi- 
ments prove  that  when  a  muscle  does  work  it  becomes 
hotter,  and  we  all  know  that  exercise  makes  us  warm. 
This  shows  that  the  oxidation  or  burning  which  takes 
place  in  a  working  muscle  does  not  all  become  turned  into 
mechanical  work,  but  a  good  share  of  it  appears  as  heat. 
What  is  true  of  muscle  is  true  of  all  other  organs  of  the 
body:  when  they  work,  no  matter  what  their  kind  of  work, 
their  substance  is  oxidized,  and  some  of  the  energy  set  free 

What  is  the  chemical  term  for  burning?   What  does  food  supply? 

Point  out  a  chief  reason  for  our  need  of  eating? 

Why  are  our  bodies  warm  ?  Why  is  it  important  that  they  should 
be  warm  ?  How  is  the  temperature  of  a  muscle  affected  when  it 
works  ?  Do  other  organs  resemble  muscles  in  this  respect? 


THE    NECESSITY    OF   FOOD  97 

by  the  oxidation  appears  as  heat,  assisting  to  keep  the 
body  warm.,  and  at  its  best  working  temperature. 

A  second  reason  why  we  need  food. — Since  the  body  only 
works  well  at  a  temperature  which  is  higher  than  that  of 
the  air  around  it  (except  on  a  very  hot  day),  and  in  health 
always  keeps  at  this  temperature,  it  must  lose  heat  nearly 
all  the  time.  At  night  each  of  us  is,  in  health,  justaswirm 
as  in  the  morning ;  and  in  the  morning  as  when  we  went 
to  bed  ;  though  we  have  lost  heat  to  the  air  during  the 
day,  and  to  the  bedclothes  at  night.  In  order  to  keep  our 
bodies  at  the  temperature  most  suitable  to  their  activity, 
they  must,  therefore,  generate  heat  all  the  time,  to  com- 
pensate for  the  giving  of  it  from  them  to  the  outer  world. 
In  this  necessity  of  generating  heat  we  find  a  second  reason 
for  the  need  of  food  :  we  require  daily  to  take  into  our- 
selves tilings  which  can  be  burned  (or  oxidized)  in  the 
body,  and  which  in  so  doing  will  give  off  heat. 

The  influence  of  starvation  upon  muscular  work  and 
animal  heat. — -When  a  man  is  deprived  of  food  the  supply 
of  things  which  can  be  oxidized  in  his  body  is  cut  off.  The 
tissues  and  organs  are  used  up  and  not  renewed  ;  his  tem- 
perature falls,  his  muscles  become  weaker  and  weaker,  and 
at  last  he  dies.  The  body  does  not  live,  and  work,  and 
keep  warm,  by  mecins  of  a  peculiar  vital  force  or  energy 
which  inhabits  it,  but  by  utilizing  the  energy  set  free  in  it 
by  the  oxidation  of  foods,  or  of  things  made  in  it  from 
foods.  If  the  food  supply  be  cut  off, the  body  first  uses  up 

What  must  we  conclude  from  the  fact  that  our  bodies  keep  at 
nearly  the  same  temperature  all  the  time?  How  do  we  know  that 
they  generate  heat?  Give  a  reason  for  taking  food,  in  addition  to  its 
use  as  a  source  of  energy  to  be  spent  by  the  muscles. 

What  happens  when  a  man  is  starving  ?  How  does  the  body  live, 
and  keep  warm,  and  work?  What  first  happens  when  the  food  sup- 
ply is  stopped? 

7 


98  THE    HUMAN   BODY. 

any  reserve  of  nutritious  matter  which  may  have  been 
stored  up  in  it  when  the  starvation  commenced,  and  as 
this  is  expended  it  becomes  weaker  and  weaker  until 
death  supervenes.  * 

How  long  a  man,  totally  deprived  of  food,  can  keep 
alive,  will  depend,  partly,  on  how  much  reserve  material, 
capable  of  oxidation,  he  has  stored  up  in  him  when  the 
starvation  period  commences ;  but  largely,  also,  on  the  ex- 
tent to  which  he  can  spare  himself  muscular  work  and 
loss  of  heat.  The  breathing  movements  and  beat  of  the 
heart  must  go  on,  but  if  the  individual  lies  quiet  in  bed 
he  need  do  little  or  no  other  muscular  work  ;  and  if  he  is 
well  covered  up  with  blankets,  the  loss  of  heat  from  the 
body  is  slight  and  calls  for  but  little  oxidation  of  the  tissues 
to  compensate  for  it.f  Also,  a  fat  person  will  survive  starva- 
tion longer  than  a  lean  one  ;  during  the  process  his  fat  is 
slowly  burnt;  but  so  long  as  it  lasts  he  can  supply  his  mus- 
cles with  something  which  can  be  oxidized  to  yield  working 
power,  and  he  also,  by  its  burning,  can  maintain  his  tem- 
perature. Fat  is,  in  fact,  a  sort  of  reserve  fuel,  laid  up  in 
the  body,  and  a  man,  in  the  strict  sense  of  the  word,  can 
hardly  be  said  to  begin  to  starve  until  his  fat  has  nearly  all 
been  used  up.J 

Upon  what  does  the  length  of  life  of  a  man  getting  no  food  de- 
pend? What  expenditures  of  energy  must  go  on  all  the  time?  How 
does  lying  in  bed  diminish  the  expenditure  of  energy?  Why  will  a 
fat  man  deprived  of  food  live  longer  than  a  lean  one? 

When  does  a  fasting  man  really  begin  to  starve? 

*  When  warm-blooded  animals  are  starved  their  temperature  slowly  falls;  and 
when  it  conies  down  to  about  77°  p.  (25°  c.)  death  occurs:  the  various  tissues  at 
that  temperature  can  no  longer  work  so  as  to  maintain  life. 

t  Hence  Dr.  Tanner,  and  "fasting  girls"  keep  in  bed,  warmly  covered  up, 
most  of  the  time:  the  losses  of  the  body  in  mechanical  work  and  heat  are  thus 
reduced  to  a  minimum,  and  consequently  the  oxidation  of  the  food  reserves  stored 
in  the  body  at  the  beginning  of  the  fast. 

t  Some  warm-blooded  animals,  as  bears,  hibernate;  that  is,  sleep  all  through 


OXIDATIONS   IN    THE   BODY.  99 

Oxidations  in  the  body. — In  the  preceding  paragraphs 
oxidation  and  burning  have  been  used  as  equivalent 
phrases  :  this  is  in  accordance  with  the  teachings  of  chem- 
istry. To  the  chemist  a  substance  is  burned  when  it  is 
combined  with  oxygen,  whether  this  combination  take  place 
slowly  or  rapidly.  If  the  combination  occur  rapidly  the 
burning  or  oxidizing  mass  becomes  very  hot  and  also  gives 
off  light:  such  a  rapid  and  vigorous  oxidation  is  called  a  com- 
bustion ;  no  combustions  take  place  in  our  bodies. 

It  has,  however,  been  proved  that  whether  the  combi- 
nation of  oxygen  with  an  oxidizable,  or  burnable)  substance 
takes  place  rapidly  or  slowly,  at  the  end  of  the  process  ex- 
actly  the  same  amount  of  energy  will  have  been  set  free  in 
each  case.  When  the  oxidation  occurs  in  a  few  seconds  the 
oxidizing  mass  becomes  very  hot :  when  it  occurs  slowly,  in 
a  few  days  or  weeks,  the  mass  will  never  be  very  hot,  be- 
cause the  heat  set  free  in  the  process  is  carried  off  nearly 
as  fast  as  it  appears.. 

Illustrations  of  oxidations  at  a  low  temperature. — If  a 
piece  of  magnesium  wire  be  ignited  in  the  air  it  will 
become  white-hot,  flame,  and  leave  at  the  end  of  a  few 


What  does  a  chemist  mean  when  he  says  a  substance  is  burned  ? 
What  is  a  combustion  ?  Do  combustions  occur  in  our  bodies  ? 

Does  the  quantity  of  energy  liberated  by  the  complete  oxidation 
of  any  substance  vary  with  the  rate  of  oxidajtion  ? 

Why  is  a  slowly  oxidizing  mass  of  matter  not  very  hot  ? 

Give  an  instance  of  the  oxidation  of  the  same  substance  at  high 
and  low  temperatures. 

the  winter  and  take  no  food.  They  feed  well  in  the  warm  weather,  and  are  quite 
fat  at  the  close  of  autumn,  when  they  seek  some  shelter od  place  to  winter  in.  This 
shelter  and  their  warm,  furry  coats  make  the  loss  of  heat  very  little;  the  animal, 
except  for  its  breathing  and  the  beat  of  its  heart,  hardly  ever  moves  during  the 
winter,  and  even  those  necessary  movements  are  reduced  to  the  least  possible,  the 
breathing  and  heart-beat  being  much  slower  than  during  the  summer.  With  return 
of  warm  weather  the  creature  wakes  up  again,  but  is  then  lean,  having  burnt  up 
its  fat  during  its  winter  sleep. 


100  TEE    HUMAN   BODY. 

seconds  only  a  certain  amount  of  incombustible  rust  or 
magnesia,  which  consists  of  the  metal  combined  with  oxy- 
gen ;  under  these  circumstances  it  has  been  burnt  or  oxid- 
ized quickly  at  a  high  temperature.  The  heat  and  light 
evolved  in  the  process  represent  the  energy  which  is  set 
free  by  the  metal  and  oxygen  when  they  combine.  We 
can,  however,  oxidize  the  metal  in  a  different  way,  attend- 
ed with  no  evolution  of  light  and  no  very  perceptible  rise 
of  temperature  If,  for  instance,  we  leave  it  in  wet  air,  it 
will  become  gradually  turned  into  magnesia  without  hav- 
ing ever  been  hot  to  the  touch  or  luminous  to  the  eye. 
The  process  then,  however,  takes  days  or  weeks  ;  but  in 
this  slow  oxidation  just  as  much  energy  is  liberated  as  in 
the  former  case,  although  now  all  takes  the  form  of  heat ; 
and  instead  of  being  liberated  in  a  short  time  is  spread 
over  a  much  longer  one,  as  the  gradual  chemical  combi- 
nation takes  place.  (The  slowly  oxidizing  magnesium  is,  in 
consequence,  at  no  moment  noticeably  hot,  since  it  loses  its 
heat  to  surrounding  objects  almost  as  fast  as  it  generates 
it.y  The  oxidations  occurring  in  our  bodies  are  of  this 
slow  kind.  An  ounce  of  arrowroot  oxidized  in  a  fire,  and 
in  the  human  body,  would  liberate  exactly  as  much  ener- 
gy in  one  case  as  the  other,  but  the  oxidation  would  take 
place  in  a  few  minutes  and  at  a  high  temperature  in  the 
former,  and  slowly,  at  a  lower  temperature,  in  the  latter. 

Oxidation  in  the  presence  of  moisture. — Wet  wood  or 
wet  coal  we  know  will  not  burn,  or  can  only  be  made  to  do 
so  with  difficulty.  Other  kinds  of  burning  or  oxidation 
are,  however,  well  known,  which  take  place  in  the  pres- 

How  does  the  rate  of  oxidation  differ  in  the  two  cases  ?  How 
does  the  oxidation  of  arrowroot  burned  in  a  fire  differ  from  its  oxida 
tion  in  the  living  body? 

Can  oxidations  occur  in  the  presence  of  moisture  '? 


OXIDATIONS  IN  THE  PRESENCE  OF  MOISTURE. 


ence  of  moisture.  The  rusting  of  iron,  for  example,  is 
an  oxidation  or  burning  of  the  metal,  and  takes  place 
faster  in  damp  air  than  in  dry;  during  the  slow  rusting  in 
moisture  just  as  much  heat  is  set  free  as  if  the  same  com- 
pound of  iron  and  oxygen  were  prepared  in  a  more  rapid 
way.  Such  experiments  throw  great  light  on  the  oxida- 
tions which  take  place  in  our  own  bodies.  All  of  them 
are  slow  oxidations,  which  never  at  any  one  moment  give 
off  a  great  amount  of  heat,  and  all  occur  in  the  damp 
tissues. 

Summary.  (1)  Energy  can  be  turned  from  one  form  in- 
to another ;  as  from  heat  into  mechanical  work  by  a  steam- 
engine.  (2)  Our  bodies  are  constantly  losing  energy,  partly 
in  muscular  work,  and  p_artly  as  heat  lost  to  surrounding 
objects.  (3)  Energy  cannot  be  created ;  all  that  can  be 
done  is  to  turn  one  kind  of  it  into  another  kind:  heat  can 
be  turned  into  mechanical  work  (as  in  a  locomotive) ;  or 
mechanical  work  into  heat  (as  by  friction)  ;  or  heat  into 
electricity  (as  in  a  thermo-electric  machine);  and  so  forth. 
(4)  Since  our  bodies  spend  energy  all  our  life  long  they 
must  be  supplied  with  it  from  outside  :  they  can  turn  into 
other  forms  the  energy  which  they  receive,  but  they  cannot 
make  it  from  nothing.  (5)  The  chief  forms  of  energy  which 
our  bodies  expend  are  muscular  (i.  e.  mechanical)  work, 
and  heat.  (6)  In  ordinary  machines,  as  a  locomotive,  the 

Give  an  instance.  Does  the  rate  of  oxidation  or  the  presence 
of  moisture  affect  the  amount  of  heat  liberated  ? 

Of  what  kind  are  the  oxidations  which  occur  in  our  bodies  ? 

Give  a  summary  of  the  contents  of  this  chapter  with  reference  to 
the  following  points:  (1)  The  transformation  of  energy;  (2)  The  loss 
of  energy  from  the  body  ;  (3)  The  fact  that  man  cannot  create  ener- 
gy but  can  transmute  it ;  (4)  The  fact  that  our  bodies  must  be  con- 
stantly supplied  with  energy  from  outside  ;  (5)  The  chief  forms  of 
energy  spent  by  the  body  ;  (6)  The,  source  of  the  energy  spent  by  a 
working  steam-engine. 


102  THE  HUMAN  BODY. 

source  of  the  work  done  and  the  heat  given  off  is  the  oxida- 
tion of  coal  in  a  furnace,  (7)  Chemistry  teaches  us  that  just 
the  same  amount  of  energy  or  work  power  is  given  off  when 
an  ounce  of  any  given  substance  is  oxidized,  whether  the 
oxidation  occurs  rapidly  or  slowly.  (8)  Chemistry  also 
teaches  us  that  many  oxidations,  or  burnings,  occur  in  the 
presence  of  water,  and  that  in  them  just  the  same  amount 
of  energy  is  set  free  as  if  the  oxidation  occurred  in  dry  air. 
(9)  In  our  bodies  substances  are  burnt  slowly  at  a  low 
temperature  and  in  the  presence  of  moisture  :  in  tliis  burn- 
ing energy  is  set  free  which  the  body  uses  for  performing 
its  necessary  work.  (10)  In  the  burning  which  the  tissues 
undergo  while  they  work  they  are  used  up  and  destroyed. 
(11)  To  compensate  for  the  destruction  of  tissue  which 
accompanies  and  provides  the  power  for  every  action  of 
the  body,  material  must  be  taken  into  it  from  outside, 
which  will  restore  or  repair  the  oxidized  tissues.  (12) 
Such  substances  taken  into  the  body  from  outside  are 
called  foods,  and  the  constant  oxidation  of  the  body  which 
is  necessitated  by  the  performance  of  the  functions  essen- 
tial to  life,  requires  a  supply  of  food  from  the  outer  world, 
if  life  is  to  be  maintained.  (13)  The  body  of  a  healthy 
person  has  in  it  at  any  moment  a  certain  reserve  of  oxid- 
izable  matters,  which  we  may  call  stored-up  food.  The 
most  important  of  these  reserve  foods  is  fat.  A  fat  man 
can  accordingly  bear  starvation  longer  than  a  lean  one  un- 
der similar  circumstances. 

(7)  The  amount  of  energy  given  off  when  a  substance  is  oxidized 
at  high  or  low  temperatures;  (8)  The  teachings  of  chemistry  with 
reference  to  oxidations  in  the  presence  of  moisture  ;  (9)  The  con- 
ditions under  which  substances  are  oxidized  in  our  bodies  ;  (10)  The 
changes  which  oxidized  tissues  undergo  ;  (11)  Why  we  need  to 
take  material  from  the  outer  world  into  our  bodies  ;  (12)  What  is 
meant  bv  food;  and  why  \v«  need  foods  ;  (13)  What  are  reserve 
foods.  Illustrate. 


THE    OXYGEN    FOOD    OF    THE    BODY.         JQ3 

(l   *>>, 
The  oxygen  food  of  the  body. — Hitherto  w&  have  only 

considered  the  energy-supply  of  the  body  from \ne  side  ; 
we  have  regarded  it  as  dependent  on  the  constant  supply 
of  things  which  can  be  oxidized.  But  this  is  only  half  the 
question  :  if  substances  are  to  be  oxidized  there  must  be  a 
provision  of  oxygen  to  oxidize  them. 

In  order  that  a  steam-engine  may  work  and  keep  warm 
it  is  not  merely  necessary  that  it  have  plenty  of  coal,  but 
it  must  also  have  a  draught  of  air  through  its  furnace. 
Chemistry  teaches  us  that  the  burning  in  this  case  consists 
in  the  combination  of  a  gas  called  oxygen,  taken  from  the 
air,  with  other  things  in  the  coals:  when  this  combination 
takes  place  a  great  deal  of  heat  is  given  off.  The  same 
thing  is  true  of  our  bodies  ;  in  order  that  food  matters 
may  be  burnt  in  them  and  enable  us  to  work  and  keep 
warm,  they  must  be  supplied  with  oxygen;  this  they  get 
from  the  air  by  breathing.  We  all  know  that  if  his  sup- 
ply of  air  be  cut  off  a  man  will  die  in  a  few  minutes.  His 
food  is  no  use  to  him  unless  he  gets  oxygen  from  the  air  to 
combine  with  it  ;  while  he  usually  has  stored  up  in  his 
body  an  excess  of  food  matters  which  will  keep  him  alive 
for  some  time  if  he  gets  a  supply  of  oxygen,  he  has  not 
stored  up  in  him  any  reserve,  or,  if  any,  but  a  very  small 
one,  of  oxygen,  and  so  he  dies  very  rapidly  if  his  breathing 
be  prevented.  In  ordinary  language  we  do  not  call  oxygen 
a  food, but  restrict  that  name  to  the  solids  and  liquids  which 
we  swallow  :  but  inasmuch  as  it  is  a  material  which  we 
must  take  from  the  external  universe  into  our  bodies  in  or- 


Why  do  we  need  oxygen  ?  What  does  a  working  steam-engine 
need  in  addition  to  coal?  What  happens  in  the  furnace  of  an  engine? 
Why  do  we  need  to  breathe  ?  What  happens  if  a  man's  air  supply 
be  stopped  ?  Why  does  a  man  die  sooner  of  want  of  air  than  of  want 
of  food  ?  Why  is'oxygec  entitled  to  be  called  a  food  ? 


104  THE    HUMAN   BODY. 

der  to  keep  us  alive,  oxygen  is  really  a  food  as  much  as  any 
of  the  other  substances  which  we  take  into  our  bodies 
from,  outside,  in  order  to  keep  them  alive  and  at  work. 
Suffocation,  as  death  from  deficient  air  supply  is  named,  is 
really  death  from  oxygen-starvation. 

What  is  suffocation? 


APPENDIX  TO  CHAPTER  VIII. 

The  liberation  of  energy  by  oxidation,  or  burning,  at  a  low  tem- 
perature and  in  the  presence  of  moisture,  is  such  a  fundamental  fact 
in  physiology,  and  its  essential  agreement  with  ordinary  combustion 
so  difficult  to  grasp  by  most  pupils,  who  naturally  associate  burning 
with  a  high  temperature  and  luminosity,  that  it  is  worth  while  to  il- 
lustrate these  facts  by  a  few  simple  experiments. 

1.  Buy  a  coil  of   magnesium  wire,  which  can  be  obtained  at  small 
cost.     Rub  it  clean  with    fine  emery  paper  :   cut  it  in  two,  apply  a 
lighted  nritch  to  one  half  and  show  how  it  is  rapidly  consumed  with 
the  evolution  of   light  and  heat,  leaving  behind  only   a  white  powder, 
magnesia,  which  is  oxidized  magnesium.     Put  the  other  half  away  in 
a  bottle  with  a  few   drops  of  water.     After   a  day  or  two  its  surface 
will  be  covered  by  a  layer  of  magnesia;  if  this  be  scraped  off  another 
will  succeed  it ;  and  so  on.      This  experiment  shows  that  oxidation 
may  occur  rapidly  at  a  high    temperature  in  a  short  time,  or  slowly 
at  a  low  temperature  in  a  long  time,  but  the  ultimate  product,  in  each 
case,  is  the  same. 

2.  In  relation  to  a  subsequent   paragraph  (p.  112)  the  magnesia  ob- 
tained by  burning  the  wire  in   the  air,  may  be  kept,  and  attempts 
made  to  ignite  it;  this  will  serve  to  show  the  uselessness  of  oxidized 
substances  to  the  body,  as  sources  of  energy  :  they  cannot  be  any 
more  oxidized,  and  the  best  thing  to  do  is  to  get  rid  of  them. 

8.  Get  a  bundle  of  iron  wire  :  rub  it  bright  with   emery  or  sand 

Fiper.  Place  some  in  a  warm  dry  bottle  by  the  stove  or  fireplace, 
ut  the  rest  in  a  bottle  containing  a  little  water.  Next  day  the  first 
specimen  will  be  found  bright,  and  the  second  covered  with  rust.  This 
shows  that  oxidation  may  sometimes  occur  better  in  the  presence  of 
water  than  in  its  absence  ;  and  serves  as  a  text  for  pointing  out  how 
oxidations  occur  in  the  moist  tissues  of  the  body. 


CHAPTER    IX. 
NUTRITION. 

The  Wastes  of  the  Body. — A  man  takes  into  his  body 
daily  several  pounds  of  foods  of  various  kinds,  as  meats, 
bread,  vegetables,  and  water,  yet  lie  grows  no  heavier;  it  is, 
therefore,  clear  that  his  body  must  in  every  twenty-four 
hours  return,  on  the  average,  to  the  outside  world  about  as 
great  a  weight  of  matter  as  it  receives  from  it.  Even  in 
childhood,  while  growth  is  taking  place  and  the  body  be- 
coming heavier,  the  gain  is  never  nearly  equal  to  the  weight 
of  the  foods  swallowed.  The  materials  given  off  daily  from 
the  body  to  the  external  universe,  and  compensating  more 
or  less  accurately  for  the  receipts  from  the  outside  world, 
are  its  wastes,  and  are  chiefly  things  which  cannot  be 
burned.  Much  of  the  food  taken  in  can  be,  and  is,  oxi- 
dized to  enable  us  to  move  and  keep  warm.  When  burned 
it  is  of  no  further  use  to  us,  and  would  only  clog  up  the 
various  organs,  as  the  ashes  and  smoke  of  an  engine  would 
soon  put  its  fire  out  if  they  were  allowed  to  accumulate  in 
the  furnace.  The  chief  wastes  of  the  body  are  carbon  di- 
oxide gas,  water,  and  a  kind  of  ammonia  called  urea.  / 

Receptive  and  Excretory  Organs. — Those  organs  of  the 
body  whose  function  it  is  to  gather  new  material  from 
outside  for  its  use  are  known  as  receptive  organs.  There 

What  facts  make  it  clear  that  a  man  must  daily  give  off  several 
pounds  weight  of  matter  from  his  body?  Does  a  child's  increase  in 
weight  equal  the  weight  of  the  food  it  has  eaten?  What  is  meant  by 
the  "wastes"  of  the  body?  How  do  most  foods  differ  from  wastes 
in  regard  to  oxidation ?  Why  must  wastes  be  removed  from  the  body? 
Name  the  chief  wastes  of  the  body. 

What  is  meant  by  the  receptive  organs? 

[105] 


106  THE  HUMAN  BODY. 

are  two  chief  sets  of  these — one  to  receive  oxidizable  things, 
and  the  other  to  receive  oxygen.  The  first  set  is  represent- 
ed by  the  alimentary  canal,  consisting  of  mouth,  gullet  * 
stomachy  and  intestines.  It  takes  in  food  and  drink.  The 
second  set  consists  of  the  lungs,  with  the  air  passages  lead- 
ing to  them  ;  their  business,  as  receptive  organs,  is  to 
absorb  oxygen. 

The  organs  whose  duty  it  is  to  get  rid  of  waste  materials 
formed  in  the  body  are  called  excretory  organs.  The  three 
most  important  excretory  organs  are  the  lungs,  the  kidneys, 
and  the  sJcin;  the  lungs  pass  carbon  dioxide  gas  out  to  the 
air,  and  also  water  ;  the  kidneys  get  rid  of  urea  and  water ; 
and  the  skin,  of  water  and  a  little  urea. 

The  Intermediate  Steps  between  Reception  and  Ex^ 
cretion. — Between  the  taking  of  oxidizable  substances  into 
our  mouths  and  oxygen  into  our  lungs,  on  the  one  hand, 
and  the  return  of  oxidized  matters  from  our  bodies  to  the 
surrounding  world  on  the  other,  a  great  many  intermediate 
steps  take  place.  The  alimentary  canal  (see  Fig.  1)  is  a 
tube  which  runs  through  the  body  but  nowhere  opens  into 
it ;  so  long  as  food  lies  in  this  tube  it  therefore  does  not 
really  form  a  part  of  the  body,  and  is  of  no  use  to  it :  it 
resembles  coals  in  the  tender  of  a  locomotive,  waiting  to  be 
transferred  to  the  furnace.  In  our  bodies  the  furnace  is 
everywhere;  wherever  there,  is  a  living  tissue  things  are 

What  are  the  functions  of  the  two  chief  sets?  Name  those  con- 
cerned in  receiving  oxidizable  things.  Those  whose  business  it  is  to 
absorb  oxygen. 

What  is  meant  by  the  excretory  organs?  ISTame  the  most  im- 
portant. What  does  each  get  rid  of? 

Why  is  food  in  the  stomach  not  really  a  part  of  the  body?  To 
what  may  we  liken  it?  Where  is  the  furnace  of  the  body?  Why 
must  food  be  carried  all  over  the  body? 

*  The  technical  name  for  the  gullet  is  cesophagut. 


NUTRITION.  107 

burned  to  enable  it  to  work;  and  the  food  or  fuel  must  be 
brought,  therefore,  to  every  corner  of  our  frames. 

Digestion. — A  great  part  of  our  food  is  solid,  and  could 
not  of  itself  get  outside  of  the  alimentary  canal.  To  render 
it  available  it  must  be  dissolved  so  that  it  can  soak  through 
the  walls  of  the  stomach  and  intestines.  For  this  purpose 
we  find  a  set  of  digestive  organs  which  make  solvent  juices 
and  pour  them  on  the  food  which  we  swallow,  and  so  get 
it  into  a  liquid  state  in  which  it  can  be  absorbed. 

Circulation. — The  solution  containing  our  digested  food 
if  it  simply  soaked  through  the  walls  of  the  alimentary 
canal,  would  be  of  no  use  to  distant  parts,  as  the  brain,  or 
the  muscles  of  the  limbs.  AVe  find,  therefore,  in  the  body 
a  set  of  tubes  containing  blood,  and  called  blood-vessels: 
the  blood  is  driven  through  these  by  a  pump,  the  heart. 
Much  of  the  dissolved  food  passes  into  the  blood-vessels  of 
the  alimentary  canal,  and  from  them  is  carried  by  other 
blood-vessels  to  every  organ,  no  matter  how  remote.  As 
the  blood  flows  unceasingly,  round  and  round  in  its  vessels, 
from  part  to  part,  the  organs-  concerned  in  moving  and 
conveying  it  are  called  circulatory  organs,  and  the  blood- 
flow  itself  is  known  as  the  circulation. 

Absorbents. — Some  of  the  dissolved  food  is  taken  up 
into  another  set  of  tubes.,  in  the  walls  of  the  alimentary 
canal;  these  tubes  carry  it  afterwards  into  the  blood-vessels. 
They  are  called  the  absorbents. 

Why  must  many  foods  be  dissolved?  What  is  accomplished  by 
the  digestive  organs? 

What  are  the  blood-vessels?  What  enters  those  of  the  alimentary 
canal?  How  are  organs  distant  from  the  alimentary  canal  nourished? 
Why  are  the  organs  which  keep  up  the  blood-flow  called  circulatory 
organs?  What  is  meant  !>y  the  circulation? 

What  are  the  ab?jrbents?  Where  do  they  convey  the  foods 
which  they  take  ;  p  in  the  walls  of  the  alimentary  canal  ? 


108  THE  HUMAN  BODY. 

Respiration. — The  blood  in  its  course  flows  through  the 
lungs.  It  is  necessary  not  merely  that  food,  but  oxygen  also 
should  be  carried  to  every  part  of  the  body.  As  the  blood 
traverses  the  lungs  it  picks  up  oxygen  from  the  air  in  them; 
this  air  is  then  renewed  by  taking  a  fresh  breath,  and  so 
on.-  The  organs  concerned  in  renewing  the  air  in  the 
lungs  are  the  respiratory  organs,  and  the  act  of  renewal  is 
respiration. 

Assimilation. — As  each  organ  works  it  oxidizes;  some  of 
its  substance  is  broken  down  by  combination  with  oxygen 
brought  to  it  by  the  blood,  and  is  thus  converted  into  burnt 
waste  matter.  The  blood,  as  we  have  seen,  brings,  how- 
ever, not  merely  oxygen,  but  also  food  matters  in  solution. 
These  ooze  through  the  walls  of  the  blood-vessels,  and  are 
taken  up  by  the  living  tissues  and  built  into  new  tissues 
like  themselves,  to  replace  the  part  which  has  been  used 
up  and  destroyed.  This  building  and  repair  of  tissues 
and  organs  from  the  dissolved  food  obtained  from  the 
blood  is  known  as  assimilation, — in  plain  English,  "a 
making  alike."  Each  living  tissue  takes  from  the  blood 
foods  which  are  not  like  itself,  and  builds  them  up  into  a 
form  of  matter  like  its  own.  The  converse  process,  which 
accompanies  all  vital  action,  the  breaking  down  into  wastes 
of  a  living  tissue  when  it  works,  is  called  dissimilation^ 
or  "a  making  unlike." 

The  Relation  of  the  Circulatory  Organs  and  the  Absorb- 
ents to  Excretion. — It  is  as  essential  to  the  body  that  its 
wastes  be  carried  off  from  the  organs,  as  that  the  used-up 

What  must  be  carried  to  all  parts  in  addition  to  food  ?  Where 
does  the  blood  get  oxygen?  What  is  meant  by  the  respiratory 
organs?  By  respiration  ? 

What  happens  when  an  organ  works?  How  are  oxidized  tissues 
replaced?  What  is  meant  by  assimilation  ?  By  dissimilation? 

What  is  needful  to  each  organ  in  addition  to  v  supply  of  fresh 
material  ? 


NUTRITION.  109 

material  be  replaced  by  new.  Not  merely  must  matter  for 
assimilation  be  provided,  but  the  various  waste  products 
must  be  removed.  Here  again  the  blood-vessels  and  ab- 
sorbents come  into  play.  Absorbents  are  found  not  only 
in  the  walls  of  the  alimentary  canal,  but  all  over  the  body. 
The  wastes  of  each  working  tissue  are  passed  out  into 
them,  and  by  them  carried  into  the  blood-vessels;  these 
in  turn  carry  the  wastes  to  the  lungs,  kidneys,  and  skin, 
which  get  rid  of  them.  The  blood  is  thus  as  important 
in  relation  to  removing  the  waste  matters  of  an  organ  as 
in  regard  to  supplying  it  with  food  and  oxygen. 

Nutrition. — From  what  has  been  said  above  it  is  clear 
that  the  nourishment  of  the  body  is  a  very  complicated 
process.  It  implies — (1)  the. reception,  of  food  from  out- 
side ;  (2)  the  digestion  of  food ;  (3)  the  absorption  of 
digested  food ;  (4)  .the  conveyance  of  absorbed  food  to  all 
parts  by  the  blood;  (5)  the_  taking  up  of  wastes  from  the 
different  organs  ;  (6)  the  conveyance  of  these  wastes  by  the 
blood  to  excretory  organs  which  pass  them  out  of  the  body  ; 
(7)  the  absorption  of  oxygen  in  the  lungs,  and  its  con- 
veyance by  the  blood  to  every  organ  ;  (8)  assimilation  or 
the  building  up  of  new  tissue  from  materials  brought  by 
the  blood  ;  and  (9)  disassimilation,  or  the  breaking  down 
of  working  tissues  by  combination  with  oxygen. 

In  subsequent  chapters  we  shall  have  to  consider  in 
more  detail,  Digestion,  Circulation,  Absorption,  Respira- 
tion, and  Excretion.  The  sum  total  of  4he  actions  of  all 
the  organs  concerned  in  the  nourishment  of  the  body  is 
known  as  the  function  of  nutrition. 

Where  do  we  find  absorbents  in  addition  to  those  of  the  alimen- 
tary canal?  What  is  their  function?  What  part  does  the  blood 
play  in  the  removal  of  wastes? 

Enumerate  the  processes  concerned  in  the  nourishing  of  the  body 

What  is  meant  by  the  function  of  nutrition? 


CHAPTER  X. 
FOODS. 

Foods  as  Tissue  Formers. — In  the  last  chapter  we  have 
considered  foods  merely  as  sources  of  energy,  but  they  are 
also  required  to  build  up  the  substance  of  the  body.  From 
birth  to  manhood  we  increase  in  bulk  and  weight,  and 
that  not  merely  by  accumulating  water  and  such  sub- 
stances, but  by  forming  more  bone,  more  muscle,  more 
brain,  and  so  on,  from  the  things  which  we  eat.  Even 
after  full  growth,  when  the  body  ceases  to  gain  weight, 
the  same  constructive  processes  go  on;  the  living  tissues 
are  steadily  oxidized  and  broken  down  as  they  work,  and  as 
constantly  reconstructed. 

Foods  are  therefore  needed,  not  only  to  supply  the  body 
with  work-power  by  their  oxidation,  but  to  supply  material 
from  which  new  living  tissue,  can  be  constructed. 

What  Foods  must  Contain. — Most  foods  serve  for  both 
purposes,  energy  supply  and  tissue  formation;  they  are 
built  up  by  the  living  cells  into  new  tissue  before  they  are 
oxidized  to  set  energy  free.  Our  food  must,  therefore, 
contain  such  substances  as  the  body  can  utilize  for  tissue 
formation.*  The  living  tissues  when  analyzed  are  found 

What  use  have  foods  besides  supplying  energy  to  the  body? 
Illustrate  from  the  growth  of  a  child.  Why  are  foods  needed  for 
construction  after  growth  has  ceased? 

What  purposes  do  most  foods  serve?  Are  they  usually  oxidized 
before  making  tissue?  What  sort  of  substances  must  our  food 
contain? 

*  Whether  anj*  food  is  ever  oxidized  in  the  body  before  being  built  up  into 
a  tissue,  as  coal  is  burnt  in  an  engine  without  ever  forming  part  of  the  engine, 
must  still  be  regarded  as  an  open  question  in  physiology.  The  old  doctrine  that 
some  foods,  as  starch  and  sugar,  were  useful  only  to  set  free  heat,  and  others, 
as  albumen  and  flesh,  alone  built  tissue,  must  be  given  up.  It  seems  certain 

[HO] 


THE  IMPORTANCE  OF  PROTEID  FOODS.         HI 

to  consist  mainly  of  carbon,  hydrogen,  nitrogen,  and  oxy- 
gen, and  we  might  at  first  suppose  that  these  chemical  ele- 
ments in  their  uncombined  form  would  serve  to  nourish 
us.  Experience,  however,  teaches  that  this  is  not  the  case. 
Four  fifths  of  the  air  is  nitrogen,  but  we  cannot  feed  on  it; 
hydrogen  gas  is  of  no  use  as  a  food;  and  a  lump  of  char- 
coal (carbon)  might  fill  the  stomach,  but  would  not  keep  a 
man  from  starving.  Oxygen  can  be  utilized  when  taken 
by  the  lungs  from  the  air;  but  all  other  elements  to  be  of 
use  as  food  must  be  taken,  not  in  their  separate  state, 
but  in  the  form  of  complex  compounds,  in  which  they  are 
chemically  combined  with  other  things;  as,  for  example, 
in  starch,  and  sugar,  and  fat,  and  oil,  and  albuminous  sub- 
stances. 

The  Special  Importance  of  Albuminous  or  Proteid  Foods. 
— All  the  active  tissues. of  the  body  are  found  to  yield  on 
chemical  analysis  large  quantities  of  proteids.  (See  p.  21). 
As  the  tissues  work  this  proteid  is  broken  down,  and  its 
nitrogen  carried  off  in  the  form  of  a  peculiar  ammoniacal 
substance,  urea;  to  repair  the  wasted  living  tissue  new 
proteids  must  be  laid  down -in  it.  So  far  as  we  know  at 
present  the  human  body  (like  that  of  most  animals)  is  un- 
able to  make  proteids  out  of  other  things;  given  one  vari- 

What  elements  do  the  tissues  yield  on  analysis  ?  Can  we  feed 
on  these  elements  in  their  uncombined  state  *?  Name  one  which  is 
absorbed  in  a  free  stale  and  used.  Whence  is  it  derived  ?  What 
organs  receive  it?  Name  substances  containing  the  necessary  elements 
in  combination  and  used  as  food. 

What  do  we  find  in  all  the  active  tissues?  What  becomes  of  the 
nitrogen  of  working  tissues?  Explain  why  proteids  are  an  essential 
article  of  diet. 

that  under  some  conditions  sugar  and  starch  may  be  used  in  building  tissue, 
though  they  cannot  do  it  alone;  but  whether  they  are  under  any  circumstances 
ever  burnt  before  making  part  of  a  tissue  is  not  certain.  On  the  other  hand, 
there  is  some  reason  to  suspect  that  albuminous  substances  may,  when  eaten 
in  excess,  be  oxidized  in  the  body  without  ever  forming  part  of  a  living  cell. 


1 1 2  THE  HUMAN  BOD  Y. 

ety  of  them  it  can  turn  it  into  other  varieties,  but  it  cannot 
make  proteids  from  things  which  are  not  proteids.  Hence 
these  albuminous  or  proteid  substances  are  an  essential 
article  of  diet. 

The  Limited  Constructive  Power  of  the  Animal  Body. — 
From  what  has  been  said  above  it  is  clear  that  our  bodies 
are,  on  the  whole,  destructive  rather  than  constructive  in 
relation  to  the  outer  world.  They  require  for  their  nutri- 
tion very  complex  chemical  compounds  (starch,  sugar,  fat, 
proteids),  build  these  up  into  living  tissues,  and  then 
oxidize  the  tissues  and  return  the  carbon,  hydrogen,  and 
nitrogen,  which  were  received  from  outside  in  the  form  of 
complicated  chemical  molecules,  to  the  outer  world  in  the 
form  of  much  simpler  chemical  compounds,  namely,  carbon 
dioxide,  water,  and  urea.  None  of  these  latter  substances 
is  capable  of  nourishing  an  animal  ;  it  cannot  from  them 
alone  build  up  its  tissues  or  set  free  energy. 

How  Plants  Supply  Food  for  Animals,  and  Animals 
Food  for  Plants. — Since  animals  are  essentially  proteid  con- 
sumers, and  destroyers  also  of  other  complex  substances, 
as  starch  and  sugar,  the  question  naturally  suggests  itself, 
How  is  it,  if  animals  are  constantly  consuming  these 
things,  that  the  supply  of  them  is  kept  up?  For  example, 
the  supply  of  proteids  ;  they  cannot  be  made  artificially 
by  any  process  known  to  us.  The  answer  is,  that  animals 
live  on  the  things  which  plants  make,  and  plants  live  on 

Do  our  bodies  on  the  whole  build  up  or  break  down  chemical 
compounds?  What  class  of  compounds  do  they  require  for  their 
nutrition?  What  do  they  do  with  these  compounds?  What  simple 
compounds  does  the  body  return  to  the  outer  world?  Can  these 
compounds  feed  any  animal? 

What  facts  suirgest  the  question,  How  is  the  supply  of  pro 
teids  nnd  other  complex  foods  kept  up?  How  is  the  question 
answered? 


FOODS.  113 

the  carbon  dioxide  and  water  and  ammonia  (urea)  which 
animals  excrete. 

As  regards  our  own  bodies  the  question  might,  indeed, 
be  apparently  answered  by  saying  that  we  get  our  proteids 
from  the  flesh  of  the  other  animals  which  we  eat.  But, 
then,  we  have  to  account  for  the  possession  of  proteids  by 
those  animals  ;  since  they  cannot  make  them  from  urea 
and  carbon  dioxide  and  water  any  more  than  we  can.  The 
animals  whose  flesh  is  used  by  us  as  food  get  their  proteids  from 
plants,  which  are  the  great  proteid  formers  of  the  world; 
the  most  carnivorous  animal  really  depends  for  its  most 
essential  foods  upon  the  vegetable  kingdom;  the  fox  that 
devours  a  hare,  in  the  long  run  lives  on  the  proteids  of 
the  herbs  that  the  hare  had  previously  eaten.* 

Non-Oxidizable  Foods. — Besides  our  oxidizable  foods  a 
large  number  of  necessary  food  materials  are  not  oxidizable, 
or  at  least  are  not  oxidized  in  the  body,  Typical  instances 
are  afforded  by  water  and  common  saU.  The  use  of  these  is 
in  great  part  physical:  the  water,  for  instance,  dissolves  ma- 
terials in  the  alimentary  canal,  and  carries  the  solutions 
through  its  walls  into  the  blood  and  lymph  vessels,  so  that 
they  can  be  conveyed  from  place  to  place  ;  and  it  permits 
interchanges  by  enabling  the  things  it  has  dissolved  to  soak 
through  the  walls  of  the  vessels.  The  salines  also  influence 
the  solubility  and  chemical  interchanges  of  other  things 
present  with  them.  Serum  albumen,  one  of  the  proteids 

Where  does  the  proteid  that  a  man  eats  in  a  piece  of  beef  come 
from?  Explain. 

What  foods  are  necessary  in  addition  to  oxidizable  ?  Give  ex- 
amples. What  are  their  physical  uses? 

*  Some  animals  are  known  which  contain  chlorophyl,  the  green  coloring 
matter  of  plant  leaves;  and  it  has  recently  been  proved  that  these  animals,  like 
plants,  can,  when  exposed  to  the  action  of  light,  live  on  the  waste  products  of 
other  animals:. 


114  THE  HUMAN  BODY. 

which  is  carried  in  the  blood  all  over  the  body  to  supply  al- 
buminous material  to  the  tissues,  is,  for  example,  insoluble 
in  pure  water,  but  dissolves  readily  if  a  small  quantity  of 
common  salt  be  present.  Besides  such  uses,  the  non-oxidiz- 
able  foods  have  probably  others,  as  what  may  be  called 
machinery  formers.  In  the  lime  salts,  which  give  their 
hardness  to  the  bones  and  teeth,  we  have  an  example  of  such 
an  employment  of  them;  and  to  a  less  extent  the  same  may 
be  true  of  other  tissues.  The  body  is  a  self-building  and 
self -repairing  machine,  and  the  material  for  this  building 
and  repair,  as  well  as  the  fuel  or  oxidizable  foods  which 
yield  the  energy  the  machine  expends,  must  be  supplied  in 
the  food.  While  experience  shows  us  that  even  for 
machinery  construction  oxidizable  matters  are  largely 
needed,  it  is  nevertheless  a  gain  to  replace  such  substances 
by  non-oxidizable  material  when  possible;  just  as,  if  prac- 
ticable, it  would  be  advantageous  to  construct  an  engine 
out  of  a  substance  which  would  not  rust,  although  other 
conditions  determine  the  selection  of  iron  for  building  the 
greater  part  of  it. 

Definition  of  Foods. — Foods  are  (I)  substances  which  are 
taken  into  the  alimentary  canal,  which  can  be  absorbed 
from  it,  and  after  absorption  serve  to  supply  material  for 
the  growth  of  the  body,  or  for  the -replacement  of  matter 
which  has  been  removed  from  it;  or  (2)  they  are  substances 
which  can  be  oxidized  in  the  body  to  yield  energy  for  its  use; 
or  (3)  substances,  which  by  dissolving  nutritive  or  waste 

Illustrate  the  use  of  common  salt  in  helping  to  keep  important 
substances  in  solution.  Illustrate  the  employment  of  nou-oxidizable 
foods  in  constructing  the  body.  What  must  foods  supply  to  the 
body  besides  fuel?  Why?  Are  oxidizable  foods  used  in  machinery 
construction?  Give  an  example  showing  the  gain  of  using  non- 
oxidizable  matters  when  possible. 

Give  a  definition  of  foods. 


DEFINITION  OF  FOODS.  115 

matters  facilitate  the  transfer  of  material  from  the  recep- 
tive organs  to  the  working,  and  from  the  working  to  the 
excretory.  Foods  to  replace  matters  which  have  been  oxi-  / 
dized  must  be  themselves  oxidizable;  they  are  force  gener-f 
ators,  but  may  be  and  generally  are  also  tissue  formers:  they 
are  nearly  always  complex  organic  substances  derived  from 
other  animals  or  from  plants.  Foods  to  replace  matters 
not  oxidized  in  the  body,  as  water  and  salt,  are  force  regu- 
lators, and  are  for  the  most  part  tolerably  simple  inorganic 
compounds.  Among  the  force  regulators  we  must,  how- 
ever, include  certain  foods,  which,  although  oxidized  in  the 
body  and  serving  as  sources  of  energy,  yet  produce  effects 
totally  disproportionate  to  the  amount  of  energy  which  they 
thus  set  free.  Their  influence  as  stimulants  in  exciting  cer- 
tain tissues  to  activity,  or  as  agents  checking  the  activity  of 
parts,  is  more  marked  than  their  direct  action  as  force  gener- 
ators. As  examples,  we  may  take  condiments:  mustard  and 
pepper  are  not  of  much  use  as  sources  of  energy,  although 
they  no  doubt  yield  some  when  oxidized;  we  take  them  for 
their  stimulating  effect  on  the  mouth  and  other  parts  of  the 
alimentary  canal,  by  which  they  promote  a  greater  flow 
of  the  digestive  secretions  or  an  increased  appetite  for  food. 
Thein,  again,  the  active  principle  of  tea  and  coffee,  is  taken 
for  its  stimulating  effect  on  the  nervous  system  rather  than 
for  the  amount  of  energy  which  is  yielded  by  its  own  oxi- 
dation. 

To  the  above  definition  of  a  food  should  be  added  the 
condition  that,  neither  the  substance  itself  nor  any  of  the 

What  foods  must  be  oxidizable?  What  are  they  called?  Do  they 
also  make  tissue?  Are  they  complex  or  simple?  What  is  their  source? 
What  is  meant  by  force  regulators?  Examples?  Are  tLey  chem- 
ically complex  or  simple?  What  oxidizable  foods  are  included 
among  the  force  regulators?  How  is  their  influence  chiefly  exhib- 
ited? Give  examples 


116  TEE  HUMAN  BODY. 

products  of  its  chemical  transformation  in  the  "body  shall  he 
injurious  to  the  structure  or  action  of  any  organ]  other- 
wise it  would  he  a  poison,  not  a  food. 

Alimentary  Principles. — The  substances  which  in  ordi- 
nary language  we  call  foods  are  in  nearly  all  cases  mixtures 
of  several  foodstuffs  with  substances  which  are  not  foods  at 
all.  Bread,  for  example,  contains  water,  salts,  gluten  (a 
proteid),  some  fats,  much  starch,  and  a  little  sugar;  all  these 
are  true  foodstuffs,  but  mixed  with  them  is  a  quantity 
of  cellulose  (the  chief  chemical  constituent  of  the  walls 
which  surround  vegetable  cells),  and  this  is  not  a  food,  since 
it  is  incapable  of  absorption  from  the  alimentary  canal. 
Chemical  examination  of  all  the  common  articles  of  diet 
shows  that  the  actual  number  of  important  foodstuffs  is 
but  small;  they  are  repeated  in  various  proportions  in  the 
different  foods  we  eat,  mixed  with  small  quantities  of  dif- 
ferent flavoring  substances,  and  so  give  us  a  pleasing 
variety  in  our  meals;  but  the  essential  substances  are  much 
the  same  in  the  fare  of  the  artisan  and  in  the  "  delicacies 
of  the  season."  The  chief  foodstuffs,  which  are  found  re- 
peated in  many  different  foods,  are  known  as  "alimentary 
principles"  and  the  nutritive  value  of  any  article  of  diet 
depends  on  the  proportion  of  these  foodstuffs  which  is 
present,  far  more  than  on  the  various  agreeable  flavoring 
matters  which  cause  certain  things  to  be  especially  sought 
after,  and  to  have  a  high  market  value.  Alimentary  prin- 
ciples may  be  conveniently  classified  into  proteids,  albu- 
minoids, hydrocarbons,  carbohydrates,  and  inorganic  bodies. 

What  is  a  poison? 

What  are  ordinary  foods?  Give  an  example.  Why  is  cellulose 
not  a  food?  What  does  chemical  examination  of  ordinary  foods 
show?  How  do  we  get  variety  in  our  foods?  What  are  "alimentary 
principles''?  On  what  does  the  nutritive  value  of  a  food  depend? 
Into  wLat  groups  are  alimentary  principles  classified? 


ALIMENTARY  PRINCIPLES.  117 

Proteid  Alimentary  Principles. — Of  the  nitrogen-contain- 
ing foodstuffs  the  most  important  are  proteids:  they  form 
an  essential  part  of  all  diets,  and  are  obtained  both  from 
animals  and  plants.  The  most  common  and  abundant  are 
myosin  and  syntonin,  which  exist  in  the  lean  of  all  meats; 
egg  albumen;  casein,  found  in  milk  and  cheese;  gluten  and 
vegetable  casein  from  various  plants. 

Albuminoid  Alimentary  Principles. — These  also  contain 
nitrogen,  but  cannot  entirely  replace  the  proteids  as  foods; 
though  a  man  can  manage  with  less  proteids  when  he  has 
some  albuminoids  in  addition.  The  most  important  is 
gelatine,  which  is  yielded  by  the  connective  tissue  and  bones 
of  animals  when  cooked.  On  the  whole  the  albuminoids 
are  not  foods  of  high  value,  and  the  calfs-foot  jelly  and 
such  compounds  often  given  to  invalids  have  not  nearly  the 
nutritive  value  they  are  commonly  supposed  to  possess. 

Hydrocarbons  (Fats  and  Oils). — The  most  important  of 
these  are  stearin,  palmatin,  margarin,  and  olein,  which  exist, 
in  various  proportions  in  animal  fats  and  vegetable  oils;  the 
most  fluid  containing  more  olein  :  butter  contains  a  pecu- 
liar fat  known  as  butyrin.  All  fats  are  compounds  of 
glycerine  with  fatty  acids,  and,  speaking  generally,  any 
such  substance  which  is  fusible  at  the  temperature  of  the 
body  will  be  useful  as  a  food.  The  stearin  of  beef  and  mut- 
ton fats  is  not  by  itself  fusible  at  the  body  temperature,  but 
is  mixed  in  those  foods  with  so  much  olein  as  to  be  melted 

What  nitrogen-containing  substances  form  an  essential  article  of 
diet?  Whence  are  they  obtained?  Name  the  most  important  proteid 
foods. 

What  foods  besides  proteids  contain  nitrogen?  To  what  extent 
can  they  take  the  place  of  proteids?  How  is  gelatin  obtained?  Should 
we  try  to  build  up  an  invalid's  strength  on  calfs-foot  jelly  alone? 
Give  the  reasons  for  your  answer. 

To  what  group  of  foods  do  fats  and  oils  belong?  Name  the  more 
important.  What  is  their  chemical  composition?  Why  are  soms 
fatty  bodies  not  nutritious?  Give  an  instance. 


118  THE  HUMAN  BODY, 

in  the  alimentary  canal.  Beeswax,  on  the  other  hand,  is  a 
fat  which  will  not  melt  in  the  intestines  and  so  passes  on 
unabsorbed,  although  from  its  composition  it  would  be  use- 
ful as  a  food  could  it  be  digested. 

Carbohydrates. — These  are  mainly  of  vegetable  origin. 
The  most  important  are  starch,  found  in  nearly  all  vege- 
table foods;  dextrin;  gums;  grape  sugar  (found  in  most 
fruits);  and  cane  sugar.  Sugar  of  milk  and  glycogen  are 
alimentary  principles  of  this  group  derived  from  animals. 
All  carbohydrates,  like  the  fats,  consist  of  carbon,  hydrogen, 
and  oxygen;  but  the  percentage  of  oxygen  in  them  is  much 
higher  than  in  fats.  When  oxidized  they  have  therefore  less 
power  of  combining  with  additional  oxygen  than  fats,  and 
so  are  not  capable  of  yielding  as  much  energy  to  the  body. 

Inorganic  Foods. — The  most  important  of  these  are 
water;  common  salt;  and  the  chlorides,  phosphates,  and 
sulphates,  of  potassium,  magnesium,  and  calcium.  A  suf- 
ficient quantity  of  most  of  these  substances,  or  of  the  ma- 
terial for  their  formation,  exists  in  all  ordinary  articles  of 
diet,  so  that  we  do  not  swallow  most  of  them  in  a  separate 
form.  Water  and  table  salt  form  exceptions  to  the  rule 
that  inorganic  bodies  are  eaten  imperceptibly  along  with 
other  things,  since  the  body  loses  more  of  each  daily  than  is 
usually  supplied  in  that  way.  It  has  been  maintained  that 
salt  as  a  separate  article  of  diet  is  an  unnecessary  luxury, 
and  there  seems  to  be  some  evidence  that  certain  savage  tribes 
live  without  more  than  they  get  in  the  meat  and  vegetables 

What  is  the  chief  source  of  carbohydrates?  Name  the  most  im 
portant.  Name  carbohydrate  foods  derived  from  animals.  How  do 
they  resemble  fats  in  composition,  and  how  do  they  differ  from  them? 
Can  an  ounce  of  starch  yield  as  much  energy  to  the  body  as  an  ounce 
of  fat?  Give  a  reason  tor  your  answer. 

Name  the  more  important  inorganic  foods.  Why  do  we  not  require 
to  eat  most  of  them  separately?  What  r.norgaoic  foods  are  taken  in 
a  separate  form?  Why? 


THE  NUTRITIVE  VALVE  OF  DIFFERENT  FOODS.    119 

which  they  eat.  Such  tribes  are,  however,  said  to  suffer 
especially  from  intestinal  parasites;  and  there  is  no  doubt 
that  to  many  animals  as  well  as  most  men  the  absence  of 
salt  from  their  diet  is  a  terrible  deprivation.  Buffaloes  and 
other  creatures  are  well  known  to  travel  miles  to  reach 
"  saltlicks;"  of  two  sets  of  oxen,  one  allowed  free  access  to 
salt,  and  the  other  given  none  save  what  existed  in  its  or- 
dinary food,  it  was  found  after  a  few  weeks  that  those  given 
salt  were  in  much  better  condition.  In  man  the  desire  for 
salt  is  so  great  that  in  regions  where  it  is  scarce  it  is  used  as 
money.  In  some  parts  of  Africa  a  small  quantity  of  salt  will 
buy  a  slave,  and  to  say  that  a  man  commonly  uses  salt  at  his 
meals  is  equivalent  to  stating  that  he  is  a  luxurious  mill- 
ionaire. In  British  India,  where  the  poorer  natives  regard 
so  few  things  as  necessaries  of  life  that  it  is  hard  to  levy  any 
excise  tax,  a  large  part  of  the  revenue  is  derived  from  a  salt 
tax,  salt  being  something  which  even  the  poorest  will  buy. 
As  regards  Europe,  it  has  been  found  that  youths  in  the 
Austrian  empire  who  have  fled  to  the  mountains  and  there 
led  a  wild  life  to  avoid  the  hated  military  conscription,  will, 
after  a  time,  though  able  abundantly  to  supply  themselves 
with  other  food  by  hunting,  come  down  to  the  villages  to 
purchase  salt,  at  the  risk  of  liberty  and  even  of  life. 

The  Nutritive  Value  of  Different  Foods.— All  meats, 
whether  derived  from  beast,  bird,  or  fish,  are  highly  valu- 
able foods.  They  contain  abundant  albumen,  more  or  less 
fat,  and,  when  cooked,  their  connective  tissue  is  in  great  part 
turned  into  gelatin.  Pork  is  the  least  easily  digested  form 
of  fresh  meat,  and  contains  a  larger  percentage  of  fat  than 
most.  This  fat,  which,  by  its  oxidation  liberates  much 

Give  illustrations  of  the  strength  of  the  desire  for  salt. 
Why  are  meats  valuable  foods?  How  does  pork  differ  from  other 
fresh  meats?     Why  is  pork  not  a  good  form  of  food  for  summer? 


120  THE  HUMAN  BODY. 

heat,  makes  it  a  good  food  in  cold  weather  for  persons  with 
a  good  digestion.  Pigs  are  especially  liable  to  a  parasite, 
called  trichina,  which  lives  in  their  muscles,  and  may  be 
transferred  thence  to  man,  sometimes  causing  death.  Hence 
pork  should  always  be  thoroughly  cooked.  Salted  meats  of 
all  kinds  are  less  digestible  and  less  nutritious  than  fresli. 
Milk  contains  an  albuminous  substance  (casein),  also  fats 
(butter),  and  a  sugar,  known  as  sugar  of  milk,  in  addition 
to  useful  mineral  alimentary  principles.  It  will  support  life 
longer  than  any  other  single  food.  Cheese  consists  essen- 
tially of  the  casein  of  milk:  it  is  a  very  nutritive  albuminous 
food.  Eggs  contain  albumens  and  fats,  and  have  a  high 
nutritive  value:  they  are  more  easily  digested  when  cooked 
soft  than  hard.  Wheat  contains  more  than  a  tenth  of  its 
weight  of  proteids,  more  than  half  its  weight  of  starch, 
some  sugar,  and  a  little  fat.  The  proteid  of  wheat  flour  is 
mainly  gluten,  which  when  moistened  with  water  forms  a 
tenacious  mass,  and  this  it  is  to  which  wheaten  bread  owes 
its  superiority.  When  the  dough  is  made,  yeast  is  added 
to  it  and  causes  fermentation  by  which,  among  other 
things,  carbon  dioxide  gas  is  produced.  This  gas,  im- 
prisoned in  the  tenacious  dough  and  expanded  by  heat  dur- 
ing baking,  forms  cavities  in  it,  and  causes  the  dough  to 
"rise"  and  make  "light  bread,"  which  is  not  only  more 
pleasant  to  eat  but  more  easily  digested  than  heavy.  Sonic1 
grains  contain  a  larger  percentage  of  starch,  but  none  have 
so  much  gluten  as  wheat;  when  bread  is  made  from  them 

Why  should  pork  be  well  cooked?  How  do  salted  meats  differ  in 
value  as  articles  of  diet  from  fresh?  What  foodstuffs  exist  in  milk? 
What  one  food  will  support  life  longest?  What  is  the  chief  aliment- 
ary principle  in  cheese?  What  is  the  nutritive  value  of  cheese?  What 
makes  the  value  of  eggs  as  foods?  Are  they  more  easilv  digested  soft 
or  hard  boiled?  What  foodstuffs  exist  in  wheat?  Why  is  wheaten 
bread  lighter  than  that  made  from  other  grains? 


ALCOHOL 


the  carbon  dioxide  gas  escapes  so  readily  from  the  less 
tenacious  dough  that  it  does  not  expand  the  mass  properly. 
Corn  contains  less  proteid,  more  starch,  and  more?  fat  than 
wheat.  Rice  is  poor  in  proteids  but  very  rich  in  starch. 
Peas  and  leans  are  rich  in  proteids  and  contain  about  half 
their  weight  of  starch.  Potatoes  are  a  poor  food.  They 
contain  a  great  deal  of  water,  and  only  about  one  part  of 
proteids,  and  fifteen  of  starch  in  a  hundred  parts  by  weight. 
Other  fresh  vegetables,  as  carrots,  turnips,  and  cabbages,  are 
valuable  mainly  for  the  salts  they  contain;  their  weight  is 
mainly  due  to  water,  and  they  contain  but  little  starch, 
proteids,  or  fats.  Fruits,  like  most  fresh  vegetables,  are 
mainly  valuable  for  their  saline  constituents,  the  other 
foodstuffs  in  them  being  only  present  in  small  proportion. 
Some  kind  of  fresh  vegetable  is,  however,  a  necessary  article 
of  diet,  as  shown  by  the  scurvy  which  used  to  prevail  among 
sailors  before  fresh  vegetables  or  lime-juice  were  supplied  to 
them. 

Alcohol.  —  We  shall  learn  later  that  all  drinks  containing 
alcohol  are  dangerous  (Chap.  XXIII.),  as  tending  to  pro- 
duce disease,  or  to  make  the  body  less  able  to  resist  it,  and 
more  dangerous  the  more  alcohol  they  contain.  For  the 
present  we  confine  ourselves  to  the  question,  Has  alcohol  a 
just  claim  to  be  called  a  food?  Does  it  build  tissue,  or 
strengthen  the  muscles,  or  help  to  maintain  our  animal 
heat?  It  may  be  useful  sometimes  as  a  medicine  when 
ordered  by  a  physician,  but  is  it  useful  to  healthy  persons 
who  can  obtain  and  digest  other  foods? 

How  does  corn  differ  from  wheat  in  composition?  What  aliment- 
ary principles  are  scarce  in  rice?  Which  one  is  abundant?  What 
do  potatoes  contain?  What  is  the  main  useful  constituent  of  most 
fresh  vegetables?  Of  fruits?  How  may  scurvy  be  prevented? 

Why  are  all  alcoholic  drinks  dangerous?  What  questions  must  be 
answered  before  deciding  if  alcohol  is  a  true  food? 


122  THE  HUMAN  BODY. 

Is  Alcohol  a  Tissue-Forming  Food  ? — To  this  the  answer 
is  certainly  no;  so  far  at  least  as  useful  tissue  is  concerned. 
It  often  leads  to  excessive  and  harmful  overgrowth  of  con- 
nective tissue  and  fat,  but  it  does  not  lead  to  development 
of  muscle  or  brain  or  gland. 

Is  Alcohol  a  Strengthening  Food  ? — To  this  the  answer  is 
also  no.  Alcohol  in  small  doses  is  a  stimulant  to  brain 
and  muscle,  and  may  for  a  short  time  excite  them  to  over- 
work or  to  work  when  they  should  be  resting.  But  as  it 
nourishes  neither  of  them,  the  final  result  is  bad.  The 
brain  and  muscle  are  left  in  an  injured  state.  As  regards 
the  brain,  the  consequence  is  often  insanity  (Chap.  XXIII.). 
As  regards  the  muscles,  very  careful  experiments  have 
been  made  on  soldiers  who  were  given  definite  tasks  to 
accomplish.  The  result  was  that  on  the  days  on  which 
they  were  supplied  with  spirits,  they  could  neither  use 
their  muscles  as  powerfully,  nor  for  as  long  a  time,  as  on 
the  days  when  they  got  no  alcoholic  drink. 

Does  Alcohol  keep  up  the  Heat  of  the  Body? — To  this 
question,  also,  the  answer  is  no,  though  this  may  seem 
strange  in  view  of  the  fact  that  a  drink  is  often  taken  "  to 
warm  one  up."  The  apparent  inconsistency  is  easily  ex- 
plained. Our  feeling  of  being  warm  depends  on  the  nerves 
of  the  skin  (p.  333).  We  have  no  nerves  which  tell  us 
whether  heart  or  muscles  or  brain  are  warmer  or  cooler. 
These  inside  parts  are  always  hotter  than  the  skin,  and  if 
blood  which  has  been  made  hot  in  them  flows  in  large 
quantity  to  the  skin,  we  feel  warmer  because  the  skin  is 


What  is  said  of  alcohol  as  a  tissue-forming  food? 

Is  alcohol  a  strengthening  food?  How  may  it  lead  to  overwork? 
Results?  What  were  the  results  of  experiments  made  on  soldiers  as 
to  the  action  of  alcohol  on  the  muscles? 

Does  alcohol  maintain  the  heat  of  the  body?  Why  does  a  drink 
sometimes  make  a  person  feel  warmer? 


TEA  AND  COFFEE.  123 

heated.  As  alcoholic  drinks  make  more  blood  flow  through 
the  skin,  they  often  make  a  man  feel  warmer.  But  their 
actual  effect  upon  the  temperature  of  the  whole  body  is  to 
decrease  it.  The  more  blood  that  flows  through  the  skin, 
the  more  heat  is  given  off  from  the  body  to  the  air,  and 
the  more  blood  so  cooled  is  sent  back  to  the  internal 
organs.  The  consequence  is  that  alcohol  cools  the  body  as 
a  whole,  though  it  may  for  a  short  time  heat  the  skin. 
That  a  large  dose  of  alcohol  leads  to  excessive  loss  of  heat 
from  the  body  has  been  proved  by  many  observations  on 
drunken  men,  and  by  experiments  on  the  lower  animals. 

The  action  of  alcohol  as  a  stimulant  is  so  much  more 
marked  than  its  efficacy  as  a  source  of  energy  that  it  is  to 
be  regarded  as  a  medicine  rather  than  a  true  food,  and  the 
best  plan  is  to  avoid  it  altogether  in  health. 

Tea  and  Coffee,  like  alcohol,  are  stimulant  rather  than 
nutritive  foods.  The  amount  of  nourishment  in  a  cup  of 
either  is  but  little.  Both  have,  however,  a  wonderful  in- 
fluence in  tranquillizing  the  nervous  system  and  removing 
the  sense  of  fatigue;  and  when  taken  in  moderate  doses 
they  usually  leave  none  of  the  injurious  after-effects  of  al- 
cohol. Some  persons,  however,  experience  wakeful  ness  or 
a  feeling  of  fulness  in  the  head  after  taking  coffee,  and 
such  should  of  course  avoid  it.  For  relieving  fatigue,  tea 
and  coffee  are  far  superior  to  alcohol.  Sportsmen  out  for 
a  long  day's  shooting  find  cold  tea  superior  to  spirits; 
military  commanders  find  a  ration  of  coffee  far  better  than 
one  of  whiskey  for  fatigued  troops,  and  all  arctic  explorers 
have  come  to  a  similar  conclusion. 

How  is  it  that  alcohol  sometimes  makes  a  person  feel  warmer? 
How  does  it  cool  the  body? 

To  what  class  of  foods  do  tea  and  coffee  belong?  What  results  do 
they  produce?  Why  are  they  better  than  alcohol  for  similar  pur- 
poses? Give  illustrations  of  the  influence  of  tea  and  coffee  in  remov- 
ing the  sensation  of  fatigue, 


124  THE  HUMAN  BODY. 

Cooking, — When  meat  is  cooked  most  of  its  connective 
tissue  is  turned  into  gelatin,  and  the  whole  mass  becomes 
softer  and  more  readily  broken  up  by  the  teeth.  In  boil- 
ing meat  it  is  a  good  plan  to  put  it  first  into  boiling  water 
which  coagulates  its  surface  layer  of  albumen,  and  this  then 
keeps  in  flavoring  and  other  matters  which  would  otherwise 
pass  out  into  the  water.  After  the  first  few  minutes  the 
cooking  should  be  continued  at  a  lower  temperature;  meat 
boiled  too  fast  is  hard,  tough,  and  stringy.  In  roasting  or 
baking  meat,  the  same  plan  is  advisable.  Put  it  close  to 
the  fire  or  in  a  hot  oven  for  a  short  time,  and  then  com- 
plete the  cooking  more  slowly  at  a  lower  temperature. 

The  cooking  of  vegetable  foods  is  of  considerable  impor- 
tance. Starch  is  the  chief  nutrient  matter  in  most  of  them, 
and  raw  starch  is  much  less  easily  digested  than  cooked. 
When  starch  is  roasted  it  is  turned  into  a  substance  known 
as  soluble  starcli,  which  is  easily  dissolved  by  the  digestive 
liquids,  so  there  is  a  scientific  foundation  for  the  common 
belief  that  the  crust  of  a  loaf  is  more  digestible  than  the 
crumb,  and  toast  than  fresh  bread. 

The  Oxidizable  Matters  required  daily  by  the  Body. — 
The  necessary  quantity  of  daily  food  depends  upon  that  of 
the  material  used  by  the  body  and  passed  out  from  it  in  each 
twenty-four  hours;  this  varies  both  in  kind  and  amount 
with  the  work  done  and  the  organs  most  used.  In  children 
a  certain  excess  is  required  to  furnish  material  for  growth. 

What  happens  when  meat  is  cooked? 

Why  does  n  good  cook  first  put  meat  that  she  is  to  boil  into  very 
hot  water?  Why  should  the  boiling  be  completed  at  a  lower  tempe- 
rature? How  should  meat  be  baked? 

Why  is  it  important  to  cook  most  vegetable  foods?  Why  is  toast 
more  easily  digested  than  fresh  bread? 

What  determines  the  necessary  amount  of  daily  food  ?  Plow  does 
it  vary?  Why  do  children  require  more  in  proportion  to  their  size 
than  adults? 


THE  ADVANTAGES  OF  A  MIXED  DIET.         125 

. 

It  is  impossible  to  state  accurately  beforehand  ju\t  what 
amount  of  food  any  individual  will  require,  but  a  genera 
idea  may  be  arrived  at  by  taking  the  average  daily  losses,  by 
excretion,  of  a  man,  as  determined  by  many  experiments 
made  on  different  persons.  Such  experiments  show  that  a 
man  of  average  size  and  doing  ordinary  work  needs  rather 
more  than  9^  ounces  (274  grams)  of  carbon  to  replace  his 
loss  of  that  element;  and  about  T77  of  an  ounce  of  nitrogen 
(20  grams).  Some  hydrogen  is  also  required,  as  the  body 
daily  loses  more  water  than  we  drink;  and  this  extra 
amount  implies  a  loss  of  hydrogen  combined  with  oxygen 
in  the  body  to  form  water. 

The  Advantages  of  a  Mixed  Diet. — Since  proteid  foods 
contain  carbon,  nitrogen,  and  hydrogen,  life  may  be  kept 
up  on  them  along  with  the  necessary  salts,  water,  and  oxy- 
gen; but  such  a  form  of  feeding  would  be  anything  but  eco- 
nomical. Ordinary  proteids  contain  in  100  parts  about  52 
of  carbon  and  15  of  nitrogen,  so  a  man  fed  on  them  alone 
would  get  about  3J  parts  of  carbon  for  every  1  of  nitrogen. 
His  daily  losses  are  not  in  this  ratio,  but  about  13.7  parts 
of  carbon  to  1  of  nitrogen;  and  so  to  get  enough  carbon 
from  proteids  far  more  than  the  necessary  amount  of  nitro- 
gen must  be  taken.  Of  dry  proteids  1  pound  2|  ounces 
(527  grams)  would  yield  the  necessary  carbon,  but  would 
contain  2|  ounces  (79  grams)  of  nitrogen,  or  four  times 
more  than  is  necessary  to  cover  the  daily  losses  of  that  ele- 
ment from  the  body.  Fed  on  a  purely  proteid  diet  a  man 
would,  therefore,  have  to  digest  a  vast  quantity  to  get 
enough  carbon,  and  in  eating  and  absorbing  it,  as  well  as 

What  is  the  average  daily  loss  of  carbon  from  the  body?  Of 
nitrogen?  Does  a  man  need  hydrogen  also  in  his  food?  Why? 

On  what  group  of  foodstuffs  can  life  be  maintained  without  any 
others?  Why  is  feeding  only  on  albuminous  substances  not  desira- 
ble? 


126  THE  HUMAN  BODY. 

in  getting  rid  of  the  excess  nitrogen  which  is  useless  to 
him,  a  great  deal  of  unnecessary  labor  would  be  thrown 
upon  the  digestive  and  excretory  organs.  Similarly,  if  a 
man  were  to  live  on  bread  alone  he  would  throw  much  un- 
necessary work  on  his  body.  For  bread  contains  but  little 
nitrogen  in  proportion  to  its  carbon,  and  so  to  get  enough 
nitrogen  far  more  carbon  than  could  be  utilized  would 
have  to  be  eaten,  digested,  and  excreted  daily. 

Accordingly  we  find  that  mankind  in  general  employ  a 
mixed  diet  when  they  can  get  it,  using  richly  proteid  sub- 
stances to  supply  the  nitrogen  needed,  but  deriving  the 
carbon  mainly  from  non-nitrogenous  foods  of  the  fatty  or 
carbohydrate  kinds,  and  so  avoiding  excess  of  either  nitrogen 
or  carbon.  For  instance,  lean  beef  contains  about  £  of  its 
weight  of  dry  proteid,  which  proteid  contains  15  per  cent 
of  nitrogen.  Consequently  1  pound  3  ounces  of  lean  meat 
would  supply  the  nitrogen  needed  to  compensate  for  a  day's 
losses.  But  the  proteid  contains  52  per  cent  of  carbon,  so 
the  amount  of  it  in  the  above  weight  of  fatless  meat  would 
be  1070  grains  (69  grams)  or  nearly  2£  ounces,  leaving  3150 
grains  (205  grams)  or  rather  more  than  seven  ounces,  to 
be  got  either  from  fats  or  carbohydrates.  The  necessary 
amount  would  be  contained  in  3940  grains  (256  grams)  or 
about  9  ounces  of  ordinary  fats,  or  in  7080  grains  (460 
grams),  a  little  over  a  pound,  of  starch;  hence  either  of  these 
with  the  above  quantity  of  lean  meat,  would  form  a  far  bet- 
ter diet  both  for  the  purse  and  the  system  than  meat  alone. 

As  already  pointed  out,  nearly  all  common  foods  contain 
s.  Good  butcher's  meat,  for  example,contains 


Explain  why  bread  by  itself  would  afford  a  bad  diet. 

Why  do  men  use  a  mixed  diet?  Explain  why  lean  meat  alone 
would  not  be  a  good  food.  How  could  the  deficient  carbon  of  lean 
beef  be  supplied? 

Give  illustrations  of  the  fact  that  most  foods  contain  more  than 
one  foodstuff. 


THE  ADVANTAGES  OF  A    MIXED  DIET.         127 

nearly  half  its  dry  weight  of  fat,  and  bread  besides  proteids 
contains  starch,  fats,  and  sugar.  In  none  of  them,  how- 
ever, are  the  foodstuffs  mixed  in  the  physiologically  best 
proportions,  and  the  practice  of  employing  several  of  them 
at  each  meal,  or  different  ones  at  different  meals  during  the 
day,  is  thus  not  only  agreeable  to  the  palate  but  in  a  high 
degree  advantageous  to  the  body.  The  strict  vegetarians 
who  do  not  employ  even  such  substances  as  eggs,  cheese, 
and  milk,  but  confine  themselves  to  a  purely  vegetable  diet, 
such  as  is  always  poor  in  proteids,  daily  take  far  more  car- 
bon than  they  require,  and  are  to  be  congratulated  on  their 
excellent  digestions  which  are  able  to  stand  the  strain. 
Those  so-called  vegetarians  who  use  eggs,  cheese,  etc.,  can 
of  course  get  on  very  well,  since  such  substances  are  ex- 
tremely rich  in  proteids,  and  supply  the  nitrogen  needed, 
without  the  necessity  of  swallowing  the  vast  bulk  of  food 
which  must  be  eaten  in  order  to  get  it  from  plants  directly. 

Why  do  we  commonly  use  several  foods  at  one  meal?  What  ele- 
ment do  strict  vegetarians  take  in  excess?  How  do  nominal  vegeta- 
rians get  their  nitrogen? 


CHAPTER  XL 
THE  DIGESTIVE  ORGANS. 

General  Arrangement  of  the  Alimentary  Canal. — The  ali- 
mentary canal  is  a  tube  which  runs  through  the  body  from 
the  lips  to  the  posterior  end  of  the  trunk.  It  is  lined  by  a 
soft  reddish  mucous  membrane  (easily  seen  inside  the  mouth), 
which  is  but  a  redder  and  moister  sort  of  skin.  'Outside 
the  mucous  membrane  are  connective  tissue  and  muscular 
layers,  which  strengthen  the  digestive  tube  and  push  the 
swallowed  food  along  it.  The  mucous  membrane  is  con- 
structed to  absorb  dissolved  nutritive  substances;  it  soaks 
them  up  and  passes  them  into  blood  or  lymph  vessels.  Im- 
bedded in  this  mucous  membrane,  or  lying  outside  it,  are 
hollow  organs  called  glands;  these  glands  make  liquids 
which  alter  chemically  many  substances  which  we  eat,  and 
turn  them  from  things  which  cannot  be  absorbed  by  the 
mucous  membrane  into  things  which  can.  The  whole  series 
of  changes  which  any  food  material  undergoes,  between  its 
reception  by  the  mouth  and  its  absorption  by  the  aliment- 
ary mucous  membrane,  is  spoken  of  as  its  digestion. 

Various  foodstuffs  undergo  different  kinds  of  changes 

"What  is  the  alimentary  canal?  By  what  is  it  liiied?  What  are 
found  outside  the  mucous  membrane  of  the  digestive  tube?  What 
are  their  uses?  With  reference  to  what  object  is  the  alimentary 
mucous  membrane  constructed?  What  does  iit  do  with  the  nutriment 
it  absorbs?  What  is  the  function  of  the  glands  of  the  alimentary 
canal?  What  is  meant  by  the  digestion  of  a  foodstuff? 

[128] 


THE  KINDS  OF  GLANDS.  129 

preliminary  to  absorption,  and  so  we  speak  of  different  kinds 
of  digestions;  as  that  of  starch,  of  fats,  of  albuminous  bodies, 
and  so  forth. 

Glands  are  hollow  organs  which  make  or  secrete  peculiar 
fluids  and  poar  them  out  on  some  free  surface  of  the  body. 
They  are  very  widely  distributed;  we  find,  for  example, 
digestive  glands  (of  several  kinds)  opening  into  the  digestive 
tube,  perspiratory  glands  opening  in  the  skin,  tear  glands 
or  lachrymal  glands  pouring  out  their  secretion  on  the  eye- 
ball. Different  glands  have  their  cavities  lined  by  different 
kinds  of  cells,  and  produce  different  secretions.  In  general 
arrangement  all  glands  are  built  on  one  or  other  of  two 
primary  structural  plans,  known  as  the  tubular  and  the 
racemose. 

The  Kinds  of  Glands. — All  portions  of  the  body  making 
and  pouring  forth  secretions  are  not  technically  called 
glands.  In  the  peritoneum,  which  lines  the  inside  of  the 
abdominal  cavity  (p.  11),  we  find  simply  a  thin  membrane 
(A,  Fig.  40),  having  on  its  side  nearer  the  cavity  which  it 
surrounds  a  layer  of  cells,  a,  and  on  its  deeper  side  a  net- 
work of  very  fine  blood-vessels,  c,  supported  by  connective 
tissue,  d.  Such  simple,  smooth,  secreting  surfaces  are  not 
common;  in  most  cases  an  extended  area  is  required  to 
form  the  necessary  amount  of  secretion,  and  if  this  were 
attained  simply  by  spreading  out  flat  membranes,  these, 
from  their  number  and  extent,  would  be  hard  to  pack  con- 
veniently in  the  body.  Accordingly,  in  most  cases,  a  large 
area  is  obtained  by  folding  the  secreting  surface  in  various 

"Why  do  we  speak  of  different  kinds  of  digestion?  Illustrate. 
What  is  a  gland?  Give  examples  of  glands.  How  do  glands  differ? 
What  are  the  two  chief  types  of  glands  named? 

Name  aud  describe  a  secreting  surface  which  is  not  technically 
called  a  gland.  What  is  gained  by  folding  a  secreting  surface? 


130 


TEE  HUMAN  BODY. 
A  B 


FIG.  40.  Forms  of  Glands.  A ,  a  simple  secreting  surf  nee:  a,  its  epithelium; 
6,  basement  membrane;  c,  capillaries:  B,  a,  simple  tubular  gland;  C',  a  secret- 
ing surface  increased  by  protrusions ;  £,  a  simple  racemose  gland;  D  and  Of, 
compound  tubular  glands;  F,  a  compound  racemose  gland.  In  all  but  A  and  B 
the  capillaries  are  omitted  for  the  sake  of  clearness.  H,  half  of  »  highly  devel- 
oped racemose  gland;  c,  its  main  duct:  " 


FORMS  OF  GLANDS.  131 

ways  so  that  a  wide  surface  can  be  packed  in  a  small  bulk, 
just  as  a  Chinese  paper  lantern  when  shut  up  occupies 
much  less  space  than  when  extended,  although  the  actual 
area  of  the  paper  in  it  remains  of  the  same  extent.  In  a 
few  cases  the  folding  takes  the  form  of  protrusions  into  the 
cavity  of  the  secreting  organ,  as  indicated  at  C,  Fig.  40,  but 
much  more  commonly  the  surface  extension  is  attained  in 
another  way,  the  supporting  or  "basement  membrane,  cov- 
ered by  its  epithelium,  being  pitted  in  or  involuted  as  at  B. 
Such  a  secreting  organ  is  known  as  a  true  gland. 

Forms  of  Glands. — In  some  cases  the  surface  involutions 
are  uniform  in  diameter,  or  nearly  so,  throughout  (B,  Fig. 
40).  Such  glands  are  known  as  tubular;  examples  are 
found  in  the  lining  coat  of  the  stomach  (Fig.  48);  also  in 
the  skin  (Fig.  76),  where  they  form  the  sweat-glands.  In 
other  cases  the  involution  swells  out  at  its  deeper  end  and 
becomes  more  or  less  sacculated  (E}\  such  glands  are  named 
racemose  or  acinous.  The  small  glands  of  the  skin  which 
form  the  oily  matter  poured  out  on  the  hairs  (p.  273)  are 
of  this  type.  In  both  kinds  the  lining  cells  near  the  deeper 
end  are  commonly  different  in  character  from  the  rest;  and 
around  that  part  of  the  gland  the  finest  and  thinnest  walled 
blood-vessels  form  a  closer  network.  These  deeper  cells 
form  the  true  secreting  tissue  of  the  gland,  and  the  tube, 
lined  with  different  cells,  leading  from  the  secreting  re- 
cesses to  the  surface  on  which  the  secretion  is  poured  out, 
and  serving  meroly  to  drain  it  off,  is  known  as  the  duct  of 
the  gland.  When  the  duct  is  undivided  the  gland  is  simple; 
but  when,  as  is  more  usual,  it  is  branched  and  each  branch 

What  is  a  tubular  gland?  Examples?  A  racemose  gland? 
Example?  Where  do  we  find  the  closest  network  of  blood-vessels 
in  a  gland?  Which  cells  of  a  gland  make  its  secretion?  What  is 
meant  by  the  "  duct"  of  a  gland?  What  is  a  simple  gland? 


132  THE  HUMAN  BODY. 

has  a  true  secreting  chamber  at  its  end  we  get  a  compound 
gland,  tubular  (G)  or  racemose  (F,  H)  as  the  case  maybe. 
In  many  cases  the  chief  duct,  in  which  the  smaller  ducts 
unite,  is  of  considerable  length,  so  that  the  secretion  is 
poured  out  at  some  distance  from  the  main  mass  of  the 
gland. 

A  fully  formed  gland,  H,  is  thus  a  complex  structure, 
consisting  primarily  of  a  duct,  c,  ductules,  dd,  and  secret- 
ing recesses,  ee.  The  ducts  and  ductules  are  lined  with 
cells  which  are  merely  protective,  and  differ  in  character 
from  the  secreting  cells  which  line  the  deepest  parts.  The 
cells  lining  the  ultimate  recesses  differ  in  different  glands, 
and  produce  different  liquids;  consequently,  though  all 
glands  are  built  on  much  the  same  plan,  they  make  very 
varied  secretions,  the  nature  of  the  secretion  of  any  gland 
depending  on  the  properties  of  its  cells. 

The  Complexity  of  the  Alimentary  Canal. — We  may 
now  return  to  our  immediate  subject,  the  alimentary  canal. 
This  is  not  a  simple  tube,  but  presents  several  dilatations  on 
its  course;  nor  is  it  a  comparatively  straight  tube,  as  dia- 
grammatically  represented  in  Fig.  1,  but,  being  much  longer 
than  the  regions  of  the  body  which  it  traverses,  much  of  it 
is  packed  away  by  being  coiled  up  in  the  abdominal  cavity. 

Subdivisions  of  the  Alimentary  Canal. — The  mouth- 
opening  leads  into  a  chamber  containing  the  teeth  and 
tongue,  and  named  the  mouth-chamber  or  ~buccal  cavity. 
This  primary  dilatation  is  separated  by  a  constriction  (the 

A  compound?  How  does  it  happen  that  the  secretion  is  some- 
times poured  out  at  a  distance  from  the  main  mass  of  the  gland? 

Describe  a  fully  developed  gland.  How  is  it  that  glands  make 
such  different  secretions?  On  what  does  the  nature  of  the  secretion 
of  a  gland  depend? 

How  does  the  alimentary  canal  differ  from  a  simple  uniform  tube? 
Why  is  a  great  part  of  it  coiled? 

Into  what  does  the  opening  bcl  ween  the  lips  lead? 


THE  MOUTH  CAVITY. 


133 


h 


isthmus  of  tlie  fauces)  at  the  back  of  the  mouth,  from 
another,  the  pharynx  or  throat 
chamber,  which  narrows  again 
at  the  top  of  the  neck  into 
i\\Q  gullet  or  oesophagus,  which 
runs  as  a  comparatively  narrow 
tube  through  the  thorax,  and 
then,  passing  through  the  dia- 
phragm, dilates  in  the  upper  rn- 
part  of  the  abdominal  cavity 
to  form  the  stomach  (see  Fig. 
1).  Beyond  the  stomach 
the  channel  again  narrows  to 
form  a  long  and  greatly  coiled 
tube,  the  small  intestine,  which 
terminates  by  opening  into  the 
large  intestine,  which,  though 
shorter  is  wider,  and  ends  by 
opening  on  the  exterior. 
The  Mouth  Cavity.  —  (Fig. 

41)  is  bounded  in  front  and  FIG.  41.—  The  mouth,  nose  and 

pharynx,  with  the  commencement  of 

Oil  the  Sides  by  the  lips  and  the  gullet  and  larynx,  as  exposed  by 

a  section,  a  little  to  the  left  of  the  me- 

Cheeks,  below  by  the  tongue,  dian  plane  of  the  head.  a,  vertebral 

7  column  ;  o,  gullet  ;  c,  windpipe  ;  a, 

*,  and  above  by  the  palate, 
which  latter  consists  of  an  an- 
terior  part,  I,  supported  by 
bone  and  called  the  hard  pal- 


er  8lde  of  the  le£t  nostrU  chamter' 


What  is  the  isthmus  of  the  fauces?  Where  does  the  gullet  begin? 
Through  what  regions  of  the  body  does  it  pass?  Where  does  the 
stomach  lie?  What  part  of  the  alimentary  canal  succeeds  the 
stomach?  Describe  it  briefly.  How  does  it  end?  How  does  the 
large  intestine  differ  from  the  small?  How  does  it  end? 

What  are  the  boundaries  of  the  mouth  cavity?  Of  what  parts 
does  the  palate  consist? 


134  THE  HUMAN  BODY. 

ate,  and  a  posterior,  f,  containing  110  bone,  and  called  the 
soft  palate.  The  two  can  readily  be  distinguished  by  ap- 
plying the  tip  of  the  tongue  to  the  roof  of  the  mouth  and 
drawing  it  backwards.  The  hard  palate  forms  the  parti- 
tion between  the  mouth  and  nose.  The  soft  palate  arches 
down  at  the  back  of  the  mouth,  hanging  like  a  curtain 
between  it  and  the  pharynx,  as  can  be  seen  on  holding  the 
mouth  open  in  front  of  a  looking-glass.  From  the  middle 
of  its  free  border  a  conical  process,  the  uvula,  hangs  down. 

The  Teeth. — Immediately  within  the  cheeks  and  lips  are 
two  semicircles,  formed  by  the  borders  of  the  upper  and 
lower  jaw-bones,  which  are  covered  by  the  gums,  except  at 
intervals  along  their  edges  where  they  contain  sockets 
in  which  teeth  are  implanted.  During  life  two  sets  of 
teeth  are  developed  :  the  first  or  milk  set  appear  soon  after 
birth  and  are  shed  during  childhood,  when  the  second  or 
permanent  set  appear. 

The  General  Structure  of  a  Tooth. — The  teeth  differ  in 
minor  points  from  one  another,  but  in  all,  three  parts  are 
distinguishable  ;*  one,  seen  in  the  mouth,  and  called  the 
crown  of  the  tooth;  a  second,  imbedded  in  the  jaw-bone, 
and  called  the  root  or  fang;  and  between  the  two,  embraced 
by  the  edge  of  the  gum,  a  narrowed  portion,  the  neck  or 
cervix.  By  differences  in  their  forms  and  uses  the 
':eeth  are  divided  into  incisors,  canines,  bicuspids,  and 

How  can  we  feel  the  difference  between  them  ?  What  cavities 
does  the  hard  palate  separate  ?  Where  does  the  soft  palate  lie  ? 
What  is  the  uvula? 

What  do  we  find  inside  the  lips  ?  Where  are  the  gums  ?  What 
do  the  margins  of  the  law  bones  contain  ?  What  are  the  inilk  teeth  ? 
What  the  permanent  V 

What  parts  may  we  distinguish  in  every  tooth?  Into  what 
groups  are  teeth  divided?  Why? 

*  A  number  of  teeth  can  be  readily  obtained  from  a  dentist,  and  will  be  found 
of  great  use  in  connection  with  thio  lesson. 


CHARACTERS  OF  INDIVIDUAL   TEETH. 


135 


molars,  arranged  in  a  definite  order  in  each  jaw.  Begin- 
ning at  the  middle  line  we  meet  in  each  half  of  each  jaw, 
successively,  with  two  incisors,  one  canine,  and  two  mo- 
lars in  the  milk  set;  making  twenty  altogether  in  the  two 
jaws.  The  teeth  of  the  permanent  set  are  thirty-two  in 
number,  eight  in  each  half  of  each  jaw,  viz. — beginning  at 
the  middle  line — two  incisors,  one  canine,  two  bicuspids, 
and  three  molars.  The  bicuspids  of  the  permanent  set 
replace  the  molars  of  the  milk  set,  while  the  permanent 
molars  are  new  teeth  added  on  as  the  jaw  grows,  and  not 
substituting  any  of  the  milk  teeth.  The  hindmost  perma- 
nent molars  are  often  called  the  ivisdom  teeth. 

Characters  of  Individual  Teeth. — The  incisors  or  cutting 


FIG.  43. 


FIG.  44. 


FIG.  42. — An  incisor  tooth. 
FIG.  43.— A  canine  or  eye  tooth. 

FIG.  44.— A  bicuspid  tooth  seen  from  its  outer  side;  the  inner  cusp  is  accord- 
ingly not  visible. 

FIG.  45. — A  molar  tooth. 

teeth  (Fig.  42)  are  adapted  for  cutting  the  food.  Their 
crowns  are  chisel-shaped  and  have  sharp  horizontal  cutting 
edges  which  become  worn  away  by  use,  so  that  they  are 
beveled  off  behind  in  the  upper  row  and  in  the  opposite 

Enumerate  the  milk  teeth  in  order.  How  many  are  there  alto- 
gether? Number  of  permanent  teeth?  Enumerate  in  order.  What 
permanent  teeth  replace  the  milk  molars?  What  permanent  teeth 
replace  no  milk  teeth?  Which  are  the  wisdom  teeth? 

Describe  an  incisor  tooth. 


136  THE  HUMAN  BODY 

direction  in  the  lower.  Each  has  a  single  long  fang.  The 
canines  (dog  teeth)  (Fig.  43)  are  somewhat  larger  than  the 
incisors.  Their  crowns  are  thick  and  somewhat  conical, 
having  a  central  point  or  cusp  on  the  cutting  edge.  Jn 
dogs  and  cats  the  canines  are  very  long  and  pointed,  and 
adapted  for  seizing  and  holding  prey.  The  bicuspids  or 
premolars  (Fig.  44)  are  rather  shorter  than  the  canines  and 
their  crowns  are  cuboidal.  Each  lias  two  cusps,  an  outer 
towards  the  cheek,  and  an  inner  on  the  side  turned  towards 
the  interior  of  the  mouth.  The  molar  teeth  or  grinders 
(Fig.  45)  have  large  crowns  with  broad  surfaces,  on  which 
are  four  or  five  projecting  tubercles  which  roughen  them 
and  make  them  better  adapted  to  crush  the  food.  Each 
has  usually  several  fangs.  The  milk  teeth  differ  only  in 
subsidiary  points  from  those  of  the  same  names  in  the  per- 
manent set. 

The  Structure  of  a  Tooth. — If  a  tooth  be  broken  open 
a  cavity  extending  through  both  crown  and  fang  will  be 
found  in  it.  This  is  filled  during  life  with  a  soft  pulp,  con- 
taining blood-vessels  and  nerves,  and  is  known  as  the 
"pulp  cavity."  The  hard  parts  of  the  tooth  disposed 
around  the  pulp  cavity  consist  of  three  different  tissues. 
Of  these,  one  immediately  surrounds  the  cavity  and  makes 
up  most  of  the  bulk  of  the  tooth;  it  is  dentine  or  ivory; 
covering  the  dentine  on  the  crown  is  enamel,  the  hardest 

A  canine.  Name  animals  with  specially  developed  canines.  For 
what  do  they  use  them?  Give  another  name  for  a  bicuspid  tooth. 
Describe  one. 

Describe  a  molar  tooth.  What  is  the  object  of  the  projections 
on  their  crowns?  How  far  do  the  milk  teeth  differ  from  the  perma- 
nent in  form? 

What  do  we  find  on  breaking  open  a  tooth?  What  is  it  called? 
Why?  What  tissues  form  the  hard  parts  of  a  tooth?  Where  does 
each  lie? 


HYGIENE  OF  THE  TEETH.  137 

tissue  in  the  body,*  and  on  the  fang  the  cement,  which  is  a 
thin  layer  of  bone. 

The  pulp  cavity  opens  below  by  a  narrow  aperture  at  the 
tip  of  the  fang,  or  at  the  tip  of  each  fang  if  the  tooth  has 
more  than  one.  Through  these  openings  its  blood-vessels 
and  nerves  enter. 

Hygiene  of  the  Teeth. — The  teeth  should  be  thoroughly 
cleansed  night  and  morning,  by  means  of  a  tooth-brush 
dipped  in  tepid  water ;  once  a  day  soap  should  be  used,  or 
a  little  very  finely  powdered  chalk  sprinkled  on  the  brush. 
The  weak  alkali  of  the  soap  or  chalk  is  useful.  A  large 
proportion  of  a  tooth  consists  of  carbonate  of  calcium,  which 
readily  dissolves  in  weak  acids  ;  and  decomposing  food 
particles  lodged  between  the  teeth  develop  acids,  which 
eat  away  the  tooth  slowly  but  surely.  Hence  all  food 
particles  should  be  carefully  removed  from  between  the 
teeth  ;  as  this  cannot  always  be  effected  completely  it  is 
important  to  brush  the  teeth  with  alkaline  substances 
which  will  neutralize  and  render  harmless  any  acid.f 
Good  manners  forbid  the  public  use  of  a  tooth-pick,  but 
on  the  earliest  privacy  after  a  meal  a  wooden  or  quill 
tooth-pick  should  be  employed  systematically  and  carefully 
to  dislodge  all  food  remnants  which  may  have  remained 
wedged  between  the  teeth. 

Where  is  the  pulp  cavity  open?  What  things  pass  through  the 
opening? 

When  and  how  should  the  teeth  be  cleansed?  What  substance 
forms  a  large  part  of  the  teeth?  In  what  is  this  substance  soluble? 
Why  should  food  particles  be  carefully  removed  from  between  the 
teeth?  Why  are  weak  alkaline  substances  useful  in  cleaning  the 
teeth? 

*  Enamel  will  strike  fire  with  flint. 

t  Acid  medicines  should  always  be  sucked  up  through  a  glass  tube  and 
swallowed  with  as  little  contact  as  possible  with  the  teeth.  After  each  dose 
the  mouth  should  be  thoroughly  rinsed  with  water. 


138 


THE  HUMAN  BODY. 


Once  a  slight  cavity  has  been  formed,  the  process  oi! 
decay  is  apt  to   go   on   very  fast ;  first,    because  the   ex- 


^  deeper  layer  of  the  tooth  is  more  easily  dissolved 
than  its  natural  surface;  and,   second,   because  the  little 


THE  TONGUE.  139 

pit  forms  a  lodging-place  for  bits  of  food,  which,  in  de- 
composing, form  acids  and  hasten  the  corrosion.  Small 
eroded  cavities  are  very  apt  to  be  overlooked  ;  the  teeth 
should,  therefore,  be  thoroughly  examined  two  or  three 
times  a  year  by  a  dentist. 

The  Tongue  (Fig.  46)  is  a  muscular  and  highly  mov- 
able organ,  covered  by  mucous  membrane,  and  endowed  not 
only  with  a  delicate  sense  of  touch,  but  with  the  sense  of 
taste.  Its  root  is  attached  to  the  hyoid  bone  (p.  26). 
The  mucous  membrane  covering  the  upper  surface  of  the 
tongue  is  roughened  by  numerous  minute  elevations  or 
papilla,  of  which  there  are  three  varieties.  The  circum- 
vallate  papillcB  (Fig.  46,  1  and  2)  are  the  largest  and  fewest, 
and  lie  near  the  root  of  the  tongue,  arranged  in  the  form 
of  a  V,  with  its  open  angle  turned  towards  the  lips.  The 
fungiform  papillae  are  rounded  masses  attached  by  nar- 
rower stems.  They  are  found  all  over  the  middle  and  fore 
part  of  the  upper  surface  of  the  tongue,  and  during  life 
are  readily  recognized  as  red  dots,  more  deeply  colored 
than  the  rest  of  the  mucous  membrane.  The  filiform 
papillce  are  pointed  elevations  scattered  all  over  the  upper 
surface  of  the  tongue,  except  near  its  root.  They  are  on 
our  tongues  the  smallest  and  most  numerous.* 

Why  is  decay  of  a  tooth  apt  to  go  on  fast  once  it  has  commenced? 
Why  should  the  teeth  be  examined  from  time  to  time  by  a  dentist? 

Briefly  describe  the  tongue.  What  sensations  do  we  obtain 
through  it?  To  what  is  its  root  attached?  What  are  found  on  the 
mucous  membrane  of  the  upper  surface  of  the  tongue?  Of  how 
many  varieties?  Which  are  largest  and  fewest?  Where  are  they 
found?  How  are  they  arranged?  Describe  the  fungiform  papillae. 
Where  are  they  found?  What  do  they  look  like  when  we  examine 
a  person's  tongue?  Where  are  the  filiform  papillae  found?  What 
is  their  form?  What  papillae  on  the  human  tongue  are  smallest? 
Most  numerous? 

*  The  filiform  papillae  are  very  large  on  the  tongue  of  the  cat,  where  they 
may  readily  be  seen  and  felt.  They  are  large  in  nearly  all  carnivorous  animals, 


140  THE  HUMAN  BODY. 

What  a  "Furred  Tongue"  Indicates.— In  health  the 
surface  of  the  tongue  is  moist,  covered  by  little  "fur" 
and,  in  childhood,  of  a  red  color.  In  adult  life  the  natural 
color  of  the  tongue  is  less  red,  except  around  the  edges 
and  tip  ;  a  bright  red  glistening  tongue  is  then  usually  a 
symptom  of  disease.  When  the  digestive  organs  are  de- 
ranged the  tongue  is  commonly  covered  with  a  thick 
yellowish  coat,  and  there  is  frequently  a  "bad  taste"  in 
the  mouth.*  The  whole  alimentary  mucous  membrane  is 
in  close  physiological  connection ;  and  anything  disorder- 
ing the  stomach  is  likely  to  produce  a  "  furred  tongue," 
which  in  most  cases  may  be  taken  as  indicating  something 
wrong  with  the  deeper  parts  of  the  digestive  tract. 

The  Salivary  Glands. — The  saliva,  which  is  poured  into 
the  mouth  and  moistens  it,  is  secreted  by  three  pairs  of 
glands,  the  parotid,  the  sulmaxillary ,  and  the  suUingual. 
The  parotid  glands  lie  close  in  front  of  the  ear  ;  each  sends 
its  secretion  into  the  mouth  by  a  duct,  which  opens  inside 
the  cheek  opposite  the  second  upper  molar  tooth.  In  the 
disease  known  as  mumps  \  the  parotid  glands  are  inflamed 
and  enlarged.  The  submaxillary  glands  lie  between  the 
halves  of  the  lower  jaw-bone,  and  their  ducts  open  beneath 

Describe  the  surface  of  a  healthy  tongue.  How  does  the  tongue 
of  a  healthy  man  differ  in  appearance  from  that  of  a  healthy  child? 
When  is  the  tongue  apt  to  be  "coated"?  "What  does  a  furred 
tongue  usually  indicate? 

By  what  is  the  saliva  secreted?  Where  does  the  paotid  gland  lie? 
Where  does  its  duct  open?  What  change  occurs  in  the  parotid 
glands  during  "mumps"?  Where  are  the  submaxillary  glands? 
Where  do  their  ducts  open? 

serving  to  scrape  or  lick  clean  bones,  etc.  Tamed  tigers  have  been  known  to 
draw  blood  by  licking  the  hand  of  their  master. 

*  The  fur  of  the  tongue  consists  of  some  mucus,  a  few  cells  shed  from  its 
surface,  and  numerous  vegetable  microscopic  organisms  belonging  to  the  group 
of  Bacteria. 

t  Technically,  parotitis. 


TEE  PHARYNX.  141 

the  tongue.  The  sublingual  glands  lie  beneath  the  floor 
of  the  mouth  behind  the  submaxillary. 

The  Fauces  is  the  name  given  to  the  passage  which 
can  be  seen  at  the  back  of  the  mouth  leading  from  it 
into  the  pharynx,  below  the  soft  palate.*  It  is  bounded 
above  by  the  soft  palate  and  uvula,  below  by  the  root  of 
the  tongue,  and  on  the  sides  by  muscles,  covered  by  mucous 
membrane,  which  reach  from  the  soft  palate  to  the  tongue. 
The  muscles  cause  elevations  known  as  the  pillars  of  the 
fauces.  Each  elevation  divides  near  the  tongue,  and  in 
the  hollow  between  its  divisions  lies  a  tonsil  (7,  Fig.  46),  a 
soft  rounded  body  about  the  size  of  an  almond,  and  con- 
taining numerous  minute  glands  which  form  mucus. 

Enlarged  Tonsils. — The  tonsils  not  unfrequently  become 
enlarged  during  a  cold  or  sore  throat,  and  then  pressing  on 
the  Eustachian  tube  (Chap.  XXI),  which  leads  from  the 
throat  to  the  middle  ear,  keep  it  closed  and  produce 
temporary  deafness.  Sometimes  the  enlargement  is  perma- 
nent and  causes  much  annoyance.  The  tonsils  can,  how- 
ever, be  readily  removed  without  danger,  and  this  is  the 
treatment  usually  adopted  in  such  cases. 

The  Pharynx  or  Throat  Cavity  (Fig.  41). — This  portion 
of  the  alimentary  canal  may  be  described  as  a  conical  bag 
with  its  broad  end  turned  towards  the  base  of  the  skull 
and  its  other  end  turned  downwards  and  narrowing  into 

Where  do  the  sublingual  glands  lie? 

What  is  meant  by  the  fauces?  How  are  they  bounded?  What 
are  the  pillars  of  the  fauces?  What  is  a  tonsil? 

Why  is  temporary  deafness  not  uncommon  when  we  have  a  sore 
throat?  What  is  usually  done  when  the  tonsils  are  permanently 
enlarged  ? 

Briefly  describe  the  pharynx.  t 

*  Observe  for  yourself  with  the  help  of  a  looking  glass. 


142  THE  HUMAN  BODY, 

the  gullet.  Its  front  or  ventral  wall  is  imperfect,  present- 
ing apertures  which  lead  into  the  nose,  the  mouth,  and 
(through  the  larynx  and  windpipe)  into  the  lungs.  Except 
when  food  is  being  swallowed  the  soft  palate  hangs  down 
between  the  mouth  and  pharynx;  during  deglutition  it  is 
raised  into  a  horizontal  position,  and  separates  an  upper  or 
respiratory  portion  of  the  pharynx  from  the  rest.  Through 
this  upper  part  air  alone  passes,*  entering  it  from  the  pos- 
terior ends  of  the  two  nostril  chambers,  while  through  the 
lower  portion  both  food  and  air  pass,  one  on  its  way  to  the 
gullet,  by  Fig.  41;  the  other  through  the  larynx,  d,  to  the 
windpipe,  c;  when  a  morsel  of  food  "goes  the  wrong  way" 
it  takes  the  latter  course.  Opening  into  the  upper  portion 
of  the  pharynx  on  each  side  is  an  Eustachian  tube,  g.  At 
the  root  of  the  tongue,  over  the  opening  of  the  larynx,  is  a 
plate  of  cartilage,  the  epiglottis,  e,  which  can  be  seen  if  the 
mouth  is  widely  opened  and  the  back  of  the  tongue  pressed 
down  by  some  such  thing  as  the  handle  of  a  spoon.  Dur- 
ing swallowing  the  epiglottis  is  pressed  down  like  a  lid  over 
the  opening  of  the  air-tube  and  helps  to  keep  food  from 
entering  it.  The  pharynx  is  lined  by  mucous  membrane 
and  has  muscles  in  its  walls  which,  by  their  contractions, 
drive  the  food  on. 

The  (Esophagus  or  Gullet  is  a  tube  commencing  at  the 

What  apertures  open  into  its  ventral  side?  What  is  the  usual 
position  of  the  soft  palate?  How  is  this  position  altered  durjng 
swallowing?  What  passes  through  the  respiratory  division  of  the 
pharynx?  What  things  pass  through  its  lower  division?  What  is 
the  destination  of  each?  What  is  meant  by  saying  a  morsel  has 
"gon,e  the  wrong  way"?  Where  do  the  Eustachian  tubes  open? 
What  is  the  epiglottis?  How  may  it  be  seen?  What  is  its  use? 

*  During  a 'severe  attack  of  vomiting  the  soft  palate  often  only  acts  imper- 
fectly in  closing  the  passage  between  gullet  and  nostrils;  hence  some  of  the 
ejected  matter  not  unfrequently  is  expelled  through  the  nose. 


THE    STOMACH. 


143 


lower  termination  of  the  pharynx  and  which,  passing  on 

through  the  neck  and  chest,  ends  below  the  diaphragm  in 

the  stomach.     In  the  neck  it  lies  close  behind  the  windpipe. 

The  Stomach  (Fig.  47)  is  a  curved  conical  bag  placed 


FIG.  47. 


FIG.  48. 


FIG  47.— The  stomach,  d,  lower  end  of  the  gullet  ;  a,  position  of  the  cardiac 
ept-rture  :  6,  the  fundus  ;  c,  the  pylcrus  ;  «,  the  first  part  of  the  small  intes- 
tine ;  along  a,  6,  c,  the  great  curvature  ;  between  the  pylorus  and  d,  the  lesser 
curvature. 

r'iG.  48. — A  thin  section  through  the  gastric  mucous  membrane,  perpendicu- 
lar to  its  surface,  magnified  about  -25  diameters,  a,  a  simple  peptic  gland;  i>,  a 
compound  peptic  gland;  c,  a  mucous  gland. 


transversely  in  the  upper  part  of  the  abdominal  cavity.* 
Its  larger  end  is  turned  to  the  left  and  lies  close  beneath 
the  diaphragm,  and  opening  into  its  upper  border,  through 
the  cardiac  orifice  at  a,  is  the  gullet,  d.  The  narrower  right 
end  is  continuous  at  c  with  the  small  intestine;  the  com- 
munication between  the  two  is  the  pyloric  orifice.  The 

Describe  the  gullet.     Where  does  it  lie  in  the  neck? 

What  is  the  stomach?  Which  end  of  it  is  larger?  Where  does 
this  end  lie?  What  opens  into  it?  What  is  the  opening  called? 
What  is  continuous  with  the  small  end  of  the  stomach?  What  is  the 
name  of  the  aperture  between  the  stomach  and  the  small  intestine? 

*  The  general  anatomical  arrangement  of  the  stomach,  and  its  connections 
with  the  gullet  and  intestine,  maybe  readily  shown  on  the  body  of  a  puppy,  kit- 
ten, or  rat,  which  has  been  killed  by  placing  it  for  five  minutes  in  a  small  box 
containing  also  a  sponge  soaked  with  chloroform. 


144  THE  HUMAN  BODY. 

pyloric  end  of  the  stomach  is  separated  from  the  diaphragm 
by  the  liver  (see  Fig.  4).  When  moderately  distended  the 
stomach  is  about  twelve  inches  long,  and  about  four  inches 
across  at  its  widest  part,  and  would  contain  about  three 
pints. 

The  Glands  of  the  Stomach. — The  mucous  membrane 
lining  the  stomach  is  seen,  when  its  surface  is  examined 
with  a  common  magnifying  glass,  to  be  covered  with  shallow 
pits.  A  more  powerful  microscope  shows  on  the  bottom 
of  each  one  of  these  pits  the  openings  of  several  minute 
tubes,  the  gastric  glands,  which  lie  imbedded  in  the  mu- 
cous membrane,  packed  closely,  sidrf'-by  side  (Fig.  48). 
These  glands  secrete  the  gastric  juice. 

The  Muscular  Coat  of  the  Stomach  lies  outside  the  mu- 
cous membrane,  and  is  made  up  (Fig.  34)  of  plain  muscular 
tissue,  whose  fibres  run  in  different  directions.  By  its 
contractions  it  stirs  up  the  food  and  mixes  it  with  the  gastric 
juice.  Around  the  pyloric  orifice  of  the  stomach  is  a  thick 
ring  of  muscle  (the  pyloric  sphincter))  which  usually  is 
contracted,  closing  the  passage  between  the  stomach  and 
the  commencement  of  the  small  intestine.  During  diges- 
tion in  the  stomach  the  pyloric  sphincter  relaxes  from  time 
to  time,  and  allows  food,  more  or  less  digested,  to  pass  on 
into  the  intestine. 

Palpitation  of  the  Heart. — The  cardiac  end  of  the  stom- 
ach lies  close  beneath  the  diaphragm,  and  the  heart  imme- 

What  lies  between  the  right  end  of  the  stomach  and  the  dia- 
phragm? What  is  the  size  of  the  stomach? 

What  may  be  seen  on  examining  the  mucous  membrane  of  the 
stomach  with  a  hand  lens?  What  does  a  more  powerful  magnify- 
ing instrument  show?  What  is  the  function  of  the  gastric  glands? 

Describe  the  muscular  coat  of  the  stomach.  What  is  its  function? 
What  is  the  pyloric  sphincter?  Its  function?  What  happens 
when  the  pyloric  sphincter  relaxes  during  gastric  digestion? 


THE  SMALL  INTESTINE. 


145 


diately  above  it.  Over-distension  of  the  stomach,  due  to 
indigestion  or  flatulency,  may  press  up  the  diaphragm 
and  interfere  with  the 
proper  working  of  the 
thoracic  organs,  causing 
feelings  of  oppression 
in  the  chest,  or  palpita- 
tion of  the  heart. 

The  Small  Intestine 
commences  at  the  pylo- 
J  rus  and  ends,  after  many 
windings,  in  the  large. 
It  is  about  twenty  feet 
(six  meters)  long  and 
about  two  inches  (five 
centimeters)  wide  at  its 
gastric  end,  narrowing 
to  about  two  thirds  of 
that  width  at  its  lower 
portion.  ;  Externally 
there  are  no  lines  of  sub- 
division on  the  small  in- 
testine, but  anatomists 
arbitrarily  describe  it  as 


FIG.  49.— Diagram  of  abdominal  part   of 
al.     C.  tlie  cardiac,  and  P,  the 


stomach;  D,  the  duode- 
num; J,  /,  the  convolutions  of  the  small  in- 
COnSlStlDg  Of  three  parts,  testine;  CO,  the  caecum  with  the  vermiform 
J.-I  o  1-1  appendix;  AC,  ascending,  TC,  transverse,  and 

the    nrst    twelve    inches    DC,  descending  colon ;  jff,  the  rectum. 

being  the  duodenum,  the  succeeding  two  fifths  of  the  re- 
mainder the  jejunum,  and  the  rest  the  ileum. 

*r 

Why  is  it  that  an  over-distended  stomach  sometimes  causes  palpi- 
tation of  the  heart? 

Where  does  the  small  intestine  commence?  Where  does  it  end? 
Describe  its  length  and  diameter.  Of  what  divisions  do  anatomists 
describe  it  as  consisting? 


146  THE  HUMAN  BODY. 

The  Mucous  Coat  of  the  Small  Intestine. — This  is  pink, 
soft,  and  extremely  vascular.  It  is  throughout  a  great  por- 
tion of  the  length  of  the  tube  raised  up  into  permanent 
transverse  folds  in  the  form  of  crescentic  ridges,  each  fold 
running  transversely  for  a  greater  or  less  way  round  the  in- 
testine (Fig.  50).  These  folds  are  the  valvulce  conniventes. 
They  are  first  found  about  two  inches  from  the  pylorus,  and 
are  most  thickly  set  and  largest  in  the  upper  half  of  the 
jejunum,  in  the  lower  half  of  which  they  become  gradually 
less  conspicuous;  they  finally  disappear  altogether  about  the 
middle  of  the  ileum.  The  folds  of  the  mucous  membrane 


FIG.  50. — A  portion  of  the  small  intestine  opened  to  show  the  valvulce  conni- 
ventes. 

serve  to  greatly  increase  its  surface  both  for  absorption  and 
secretion,  and  they  also  delay  the  food  in  its  passage;  it 
collects  in  the  hollows  between  them,  and  so  is  longer  ex- 
posed to  the  action  of  the  digestive  liquids. 

The  Villi. — Examined  closely  with  the  eye  or,  better,  with 
a  hand  lens,  the  mucous  membrane  of  the  small  intestine  is 
seen  not  to  be  smooth  but  shaggy,  being  covered  everywhere 
(both  over  the  valvulse  conniventes  and  between  them)  with 
closely  packed  minute  elevations  standing  up  somewhat  like 

Give  the  general  characteristics  of  the  mucous  membrane  of  the 
small  intestine.  What  are  the  valvulse  conniventes?  Where  do 
they  commence?  Where  are  they  most  developed?  Where  do  they 
cease?  What  purposes  do  they  subserve?  What  are  the  villi? 


THE  VILLL 


147 


the  "  pile"  on  velvet  and  known  as  the  villi  (Fig.  51).  In 
structure  a  villus  is  somewhat  complex.  Covering  it  is  a 
single  layer  of  cells,  beneath  which  the  villus  may  be  re- 
garded as  made  up  of  a  framework  of  connective  tissue  sup- 
porting the  more  essential  constituents.  Near  the  surface 
is  a  network  of  plain  muscular  tissue.  In  the  centre  is  an 
offshoot  of  the  lymphatic  or  absorbent  system,  sometimes 


FIG.  51.— Villi  of  the  small  intestine;  magnified  about  80  diameters.  In  the 
left-hand  figure  the  lacteals,  a,  6,  c,  are  filled  with  white  injection;  d.  blood  ves- 
sels. In  the  right-hand  figure  the  lacteals  alone  are  represented,  filled  with  a 
dark  injection.  The  epithelium  covering  the  villi,  and  their  muscular  fibres  are 
omitted. 

in  the  form  of  a  single  vessel  with  a  closed  dilated  end,  and 
sometimes  as  a  network  formed  by  two  main  vessels  with 
cross-branches.  During  digestion  these  lymphatics  are 
filled  with  a  milky  white  liquid  absorbed  from  the  intestines, 
and  they  are  accordingly  called  the  lacteals.  They  com- 
municate with  larger  branches  in  the  outer  coats  of  the  in- 

Describe  the  structure  of  a  villus.  What  is  found  in  its  lymphatics 
during  digestion? 


148  THE  HUMAN  BODY. 

testine,  and  these  end  in  trunks  which  join  the  main  lym- 
phatic system.  Finally,  in  each  yfflusy/ outside  its  lacteals 
and  beneath  its  muscular  layer,  is  a  close  network  of  blood- 
vessels. 

The  Glands  of  the  Small  Intestine. — Opening  on  the 
surface  of  the  small  intestine  between  the  bases  of  the  villi 
are  small  glands,  the  crypts  of  Lieberkulm.  Each  is  a 
simple  unbranched  tube,  lined  by  a  single  layer  of  cells. 

The  Muscular  Coat  of  the  Small  Intestine  lying  outside 
the  mucous  coat,  is  composed  of  plain  muscular  tissue,  dis- 
posed in  two  layers:  an  inner  circular,  and  an  outer  longi- 
tudinal. By  their  combined  and  alternating  contractions 
they  slowly  force  the  digesting  food  along  the  tube. 

In  the  duodenum  are  found  in  addition  minute  glands, 
the  glands  of  Brunner,  which  lie  outside  the  mucous 
membrane,  and  send  their  ducts  through  it  to  open  on  its 
inner  surface. 

The  Large  Intestine  (Fig.  49),  forming  the  final  portion 
of  the  alimentary  canal,  is  about  5  feet  (1.5  meters)  long, 
and  varies  in  diameter  from  2J  to  1 J  inches  (6-4  centi- 
meters). Anatomists  describe  it  as  consisting  of  the  ccecum 
(cc)  with  its  vermiform  appendix,  the  colon  (AC,  TC,  DC), 
and  the  rectum  (R).  The  small  intestine  does  not  open  into 
the  end  of  the  large  but  into  its  side,  some  distance  from 
its  closed  upper  end;  the  caecum  is  that  part  of  the  large 
intestine  which  extends  beyond  the  communication.  From 
it  projects  the  vermiform  appendix,  a  narrow  tube  not 
thicker  than  a  cedar  pencil,  and  about  4  inches  (10  centi- 

Where  do  we  find  the  crypts  of  Lieberkulm?  Describe  them. 
Where  are  the  glands  of  Brunner? 

Give  the  dimensions  of  the  large  intestine.  Of  what  parts  is  it 
made  up?  How  does  the  small  intestine  open  into  it?  What  is  the 
ca3cum?  The  vermiform  appendix?  Its  size? 


THE   LIVER,  149 

meters)  long.  The  colon  commences  on  the  right  side  of 
the  abdominal  cavity  where  the  small  intestine  communi- 
cates with  the  large,  runs  up  for  some  way  on  that  side 
(ascending  colon],  then  crosses  the  middle  line  (transverse 
colon)  below  the  stomach,  and  turns  down  (descending  colon) 
on  the  left  side,  and  there  makes  an  S-shapcd  bend  known 
as  the  sigmoid  flexure;  from  this  the  rectum  proceeds  to 
the  opening  by  which  the  intestine  communicates  with  the 
exterior.  The  mucous  coat  of  the  large  intestine  possesses 
no  villi  nor  valvulae  conniventes;  it  contains  numerous  closely 
set  glands  much  like  the  crypts  of  Lieberkiilm  of  the  small 
intestine. 

The  Ileo-Colic  Valve. — Where  the  small  intestine  joins 
the  large  there  is  a  valve  formed  by  two  flaps  of  the  mucous 
membrane  sloping  down  into  the  colon,  and  so  arranged  as 
to  allow  matters  to  pass  readily  from  the  ileum  into  the 
large  intestine,  but  not  the  other  way. 

The  Liver. — Besides  the  secretions  formed  by  the  glands 
imbedded  in  its  walls,  the  small  intestine  receives  those  of 
two  large  glands,  the.  liver  and  pancreas,  which  lie  in  the 
abdominal  cavity.  The  ducts  of  both  open,  by  a  common 
aperture,  into  the  .duodenum  about  4  inches  (10  centime- 
ters) from  the  pylorus. 

The  liver  is  the  largest  gland  fn  the  body,  weighing 
from  50  to  60  ounces  (1400  to  1700  grams).  It  is 

Describe  the  colon.  What  is  the  sigmoid  flexure?  What  is  the 
terminal  portion  of  the  alimentary  canal  named?  How  does  the 
mucous  lining  of  the  large  intestine  differ  from,  and  how  does  it  re- 
semble that  of  the  small  ? 

Where  is  the  ileo-colic  valve?  How  is  it  formed?  What  is  its 
function? 

What  large  glands  pour  their  secretion  into  the  small  intestine? 
Where  are  they  situated?  Where  do  their  ducts  open? 

What  is  the  largest  gland  in  the  body?  What  is  its  weight? 
Where  is  it  placed? 


150 


THE  HUMAN  BODY. 


situated  in  the  upper  part  of  the  abdominal  cavity  (le,  le', 
Fig.  4),  rather  more  on  the  right  than  on  the  left  side,  imme- 
diately below  the  diaphragm.  The  liver  is  of  dark  reddish- 
brown  color,  and  of  soft  friable  texture.  The  vessels  carrying 
blood  to  the  liver  (Fig.  52)  are  the  portal  vein,  Vp,  (p.  208) 
and  the  liepatic  artery;  both  enter  it  at  a  groove  on  its  under 


Dch 


Lv 


FIG.  52  —The  under  surface  of  the  liver,    d,  rfeht,  and  s,  left  lobe;  Vh.  hepa- 
10  vein;  Pp,  portal  vein;  Fc,  vena  cava  inferior;  Dch.  common  bile  duct;  DC 
cystic  duct;  Dh,  hepatic  duct;  F/,  gall-bladder. 

side,  and  there  also  a  duct  passes  out  from  each  half  of  the 
organ.  The  ducts  unite  to  form  the  liepatic  duct,  Dh, 
which  meets  the  cystic  duct,  DC,  proceeding  from  the  gall- 
bladder, Vf,  a  pear-shaped  sac  in  which  the  bile  or  gall 
formed  by  the  liver  accumulates  when  food  is  not  being  di- 
gested in  the  intestine.  The  common  bile  duct,  Dch,  formed 

Describe  the  color  and  texture  of  the  liver.  What  vessels  brin°- 
blood  to  it?  Describe  the  arran«-ement  of  its  ducts.  What  is  the 
gall-bladder?  Where  does  the  common  bile  duct  open? 


THE  PANCREAS.  151 

by  the  union  of  the  hepatic  and  cystic  ducts,  opens  into 
the  duodenum. 

The  Functions  of  the  Liver. — The  size  of  the  liver  is 
related  to  the  fact  that  the  organ  plays  a  double  function ; 
on  the  one  hand  it  is  a  digestive  gland  secreting  bile;  on  the 
other,  its  cells  serve  to  store  up,  in  the  form  'of  a  kind  of 
animal  starch,  called  glycogen,  excess  of  starchy  or  sugary 
food  absorbed  from  the  intestine  during  the  digestion  of  a 
meal,  and  then  to  gradually  dole  this  out  to  the  blood  for 
general  use  by  the  organs  of  the  body  until  the  next  meal 
is  eaten. 

The  Pancreas  or  Sweetbread*  is  a  compound  racemose 
gland.  It  is  an  elongated  soft  organ  of  a  pinkish-yellow 
color,  lying  along  the  lower  border  of  the  stomach.  Its 
right  end  is  embraced  by  the  duodenum  which  there 
makes  a  curve  to  the  left.  A  duct  traverses  it  and  joins 
the  common  bile-duct  close  to  its  intestinal  opening.  The 
pancreMs  secretes  a  watery-looking  liquid,  much  like  saliva 
in  appearance,  which  is  of  great  importance  in  digestion. 

With  what  fact  is  the  large  size  of  the  liver  connected?  What  are 
its  functions? 

To  what  group  of  glands  does  the  pancreas  belong?  Describe  its 
form  and  color.  Where  is  it  placed?  AVhatdoes  its  duct  unite  with? 
What  does  its  secretion  look  like?  Is  it  of  much  value? 

*  Butchers  sell  two  kinds  of  sweetbread,  known  as  the  belly  sweetbread  and 
the  neck  or  heart  sweetbread.  The  former  is  the  pancreas;  the  latter  is  the 
thyniuSj  an  organ  of  doubtful  function,  found  only  in  young  animals,  and  lying 
at  the  bottom  of  the  neck  and  upper  part  of  the  chest  in  front  of  the  windpipe. 


CHAPTER  XII. 

DIGESTION. 

The  Object  of  Digestion. — Some  of  the  foodstuffs  which 
we  eat  are  already  in  solution  and  ready  to  soak  at  once 
into  the  lymphatics  and  blood-vessels  of  the  alimentary 
canal;  others,  such  as  a  lump  of  sugar,  though  not  dis- 
solved when  put  into  the  mouth,  are  readily  soluble  in  the 
liquids  found  in  the  alimentary  canal  and  need  no  further 
digestion.  In  the  case  of  many  most  important  foodstuffs, 
however,  special  chemical  changes  hare  "to  be  brought 
about  to  make  them  soluble  and  capable  of  absorption. 
The  different  secretions  poured  into  the  alimentary  tube 
act  in  various  ways  upon  different  foodstuffs,  simply  dis- 
solving some  and  chemically  changing  others,  until  at  last 
all  are  got  into  a  condition  in  which  they  can  be  taken  up 
into  the  lymph  and  blood-vessels  for  transference  to  distant 
parts  of  the  body. 

The  Saliva. — The  first  solvent  poured  upon  the  food  is 
the  saliva,  which,  when  it  meets  the  food,  is  a  mixture 
of  pure  saliva  with  the  mucus  secreted  by  the  membrane 
lining  the  mouth.  This  mixed  saliva  is  a  colorless,  cloudy, 
feebly  alkaline  liquid. 

The  Uses  of  Saliva  are  mainly  physical  and  mechanical. 
It  keeps  the  mouth  moist  and  allows  us  to  speak  with  corn- 
Explain  the  object  of  digestion. 

What  is  the  first  digestive  liquid  which  the  food  meets  with? 
How  does  it  differ  from  pure  saliva?  Describe  mixed  saliva. 

[152] 


THE  USES  OF  SALIVA.  153 

fort ;  most  young  orators  know  the  distress  occasioned  by 
the  suppression  of  the  salivary  secretion  through  nervous- 
ness, and  the  imperfect  efficacy  under  such  circumstances 
of  the  traditional  glass  of  water  placed  beside  public 
speakers.  The  saliva  also  enables  us  to  swallow  dry  food; 
such  a  thing  as  a  cracker  when  chewed  would  give  rise 
merely  to  a  heap  of  dust,  impossible  to  swallow,  were  not 
the  mouth  cavity  kept  moist.*  The  saliva  also  dissolves 
such  bodies  as  salt  and  sugar,  when  taken  into  the  mouth 
in  a  solid  form,  and  enables  us  to  taste  them;  undissolved 
substances  are  not  tasted,  a  fact  which  any  one  can  verify 
for  himself  by  wiping  his  tongue  dry  and  placing  a  frag- 
ment of  sugar  upon  it.  No  sweetness  will  be  felt  until  a 
little  moisture  has  exuded  and  dissolved  part  of  the  sugar. 
Chemical  Action  of  the  Saliva. — In  addition  to  such 
actions  the  saliva,  however,  exerts  a  chemical  one  on  an 
important  foodstuff.  Starch  (although  it  swells  up  greatly 
in  hot  water)  is  insoluble  and  could  not  be  absorbed  from 
the  alimentary  canal.  The  saliva  has  the  power  of  turning 
starch  into  the  readily  soluble  and  absorbable  grape  sugar, 
the  sugar  of  most  fruits.f  The  starch  is  made  to  combine 
with  the  elements  of  water,  and  the  final  result  is  grape 
sugar. 

Describe  and  illustrate  the  uses  of  saliva  with  reference  (1)  to 
speech,  (2)  to  swallowing,  (3)  to  dissolving  some  foods. 

What  foodstuff  does  saliva  act  upon  chemically?  What  change 
is  produced  by  its  action? 

*  This  fact  used  to  be  taken  advantage  of  in  the  East  Indian  rice  ordeal  for 
the  detection  of  criminals.  The  guilty  person  believing  firmly  that  he  cannot 
swallow  the  parched  rice  given  him,  and  sure  of  detection,  is  apt  to  have  his 
salivary  glands  paralyzed  by  fear,  and  so  does  actually  become  unable  to  swal- 
low the  rice;  while  in  those  with  clear  consciences  the  nervous  system,  acting 
normally,  excites  the  usual  reflex  secretion,  and  the  dry  food  causes  no  difficulty 
of  deglutition. 

t  Grape  sugar  or  glucose  is  now  an  extensively  produced  article  of  commerce, 
being  made  for  this  purpose  by  the  prolonged  action  of  dilute  acids  upon 
starchy  substances. 


154  THE  HUMAfl  BODY. 

C12Hao010  +  2H20    =    2C6H13Ofl 

Starch.  Water.  Grape  Sugar. 

The  Influence  of  Saliva  in  Promoting  Digestion  in  the 
Stomach. — So  far  as  chemical  changes  are  concerned  the 
saliva  is  but  of  secondary  importance  in  digestion:  its  main 
use  is  to  facilitate  swallowing.  It  only  changes  starch  into 
grape  sugar  (at  least  rapidly)  when  no  acid  is  present,  and 
food  passes  from  the  mouth  to  the  stomach  where  it  is 
mixed  with  the  acid  gastric  juice,  before  the  saliva  has  time 
to  do  much.  Indirectly,  however,  the  saliva  promotes  di- 
gestion in  the  stomach.  Weak  alkalies  stimulate  the  gastric 
glands  to  pour  forth  more  abundant  secretion,*  and  the 
saliva,  being  alkaline,  acts  in  this  way.  This  is  one  reason 
why  food  should  be  well  chewed  before  being  swallowed; 
its  taste,  and  the  movements  of  the  jaws,  excite  a  more 
abundant  salivary  secretion,  and  this  alkaline  saliva,  when 
swallowed,  helps  to  stir  the  stomach  up  to  work. 

Swallowing  or  Deglutition. — A  mouthful  of  solid  food 
is  broken  up  by  the  teeth  and  rolled  about  the  mouth  by 
the  tongue  until  it  is  thoroughly  mixed  with  saliva  and 
made  into  a  soft  pasty  mass.  The  muscles  of  the  cheeks 
keep  this  from  getting  between  them  and  the  gums.f  The 
mass  is  finally  sent  on  from  the  mouth  to  the  stomach  by 

What  is  the  chief  use  of  saliva?  Under  what  circumstances  does 
it  change  starch  into  sugar?  In  what  portion  of  the  digestive  tract 
is  this  action  of  the  saliva  stopped?  Why?  How  does  the  saliva 
promote  digestion  in  the  stomach?  Why  should  food  be  thoroughly 
chewed  before  swallowing? 

What  is  the  technical  term  for  swallowing?  In  how  many  stages 
does  swallowing  occur? 

*  Hence  the  efficacy  of  a  little  carbonate  of  soda  or  apollinaris  water  taken 
before  meals,  in  some  forms  of  dyspepsia. 

t  Persons  with  facial  paralysis  have  from  time  to  time  to  press  out  with  the 
finger  food  which  has  collected  outside  the  gums,  where  it  can  neither  be  chewed 
nor  swallowed. 


DEGLUTITION.  155 

J^  a  Mf  S/ 

the  process  of  deglutition,  which  occurs  in  three  stages. 
The  first  stage  includes  the  passage  from  the  mouth  into 
the  pharynx.  The  food  being  collected  into  a  heap  on  the 
tongue,  the  tip  of  that  organ  is  placed  against  the  front  of 
the  hard  palate,  and  then  the  rest  of  the  tongue  is  raised 
from  before  back,  so  as  to  compress  the  food  mass  between  it 
and  the  palate  and  drive  it  through  the  fauces.  This  much 
of  the  act  of  swallowing  is  voluntary,  or  at  least  is  under 
the  control  of  the  will,  although  it  commonly  takes  place 
unconsciously.  The  second  stage  of  deglutition  is  that  in 
which  the  food  passes  through  the  pharynx;  it  is  the  most 
rapid  part  of  its  progress,  since  the  pharynx  has  to  be 
emptied  quickly  so  as  to  clear  the  opening  of  the  air-pas- 
sages for  breathing  purposes.  The  food  mass,  passing  back 
over  the  root  of  the  tongue,  pushes  down  the  epiglottis  ;  at 
the  same  time  the  larynx  (or  voice-box  at  the  top  of  the 
windpipe)  is  raised  so  as  to  meet  the  epiglottis,  and  thus 
the  passage  to  the  lungs  is  closed.*  The  soft  palate  is,  at 
the  same  time,  moved  into  a  horizontal  position,  so  as  to 
separate  the  upper  (or  respiratory)  portion  of  the  pharynx, 
leading  to  the  nose  and  the  Eustachian  tubes  (see  Fig.  41), 
from  its  lower  portion,  which  ends  inferiorly  in  the  gullet. 
Finally  the  isthmus  of  the  fauces  is  closed  as  soon  as 
the  food  has  passed  through,  by  the  contraction  of  the 
muscles  on  its  sides,  and  the  elevation  of  the  root  of  the 
tongue.  All  passages  out  of  the  pharynx  except  the  gullet 
being  thus  blocked,  when  the  pharyngeal  muscles  contract 

Describe  the  first  stage.  What  is  the  second  stage?  Which 
stage  is  most  rapid?  Why?  How  is  the  passage  to  the  lungs 
closed  while  food  is  passing  through  the  pharynx?  How  is  the 
passage  to  the  nose  blocked?  Describe  the  processes  of  the  second 
stage  of  deglutition. 

*  The  raising  of  the  larynx  during  swallowing  can  be  readily  felt  by  placing 
the  finger  on  its  large  cartilage  forming  "Adam's  apple"  in  the  neck. 


156  THE  HUMAN  BODY 

the  food  can  only  be  squeezed  into  the  oesophagus.  The 
muscular  movements  concerned  in  this  part  of  deglutition 
are  all  excited  without  the  intervention  of  the  will;  food 
touching  the  mucous  membrane  of  the  pharynx  produces 
quite  involuntarily  the  proper  action  of  the  swallowing 
muscles.*  Indeed,  many  persons  after  having  got  the 
mouth  completely  empty  cannot  perform  the  movements 
of  the  second  stage  of  deglutition  at  all.  On  account  of 
the  involuntary  nature  of  the  contractions  of  the  pharynx 
any  food  which  has  once  entered  it  must  be  swallowed;  the 
isthmus  of  the  fauces  forms  a  sort  of  Rubicon;  food  that 
has  entered  the  pharynx  must  be  swallowed,  even  although 
the  swallower  learned  immediately  that  he  was  taking  poi- 
son. The  third  stage  of  deglutition  is  that  in  which  the 
food  is  passing  along  the  gullet,  and  is  comparatively  slow. 
Even  liquid  substances  do  not  fall  or  flow  down  this  tube, 
but  have  their  passage  controlled  by  its  muscular  coats, 
which  grip  the  successive  portions  swallowed  and  pass 
them  on.  Hence  the  possibility  of  performing  the  appar- 
ently wonderful  feat  of  drinking  a  glass  of  water  while 
standing  upon  the  head,  olten  exhibited  by  jugglers;  peo- 
ple forgetting  that  one  sees  the  same  thing  done  every 
day  by  horses  and  other  animals  which  drink  with  the 
pharyngeal  end  of  the  gullet  lower  than  the  stomach. 

The  Gastric  Juice. — The  food  having  entered  the  stom- 
ach is  exposed  to  the  action  of  the  gastric  juice,  which  is  a 
thin  colorless  or  pale  yellow  liquid  of  a  strongly  acid  re- 
action. It  contains,  beside  water  and  some  salts  and  mu- 

How  are  the  movements  of  the  second  stage  of  deglutition  excited? 
What  is  the  third  sta^e  of  deglutition?  Is  it  fast  or  slow?  How  is 
it  that  jugglers  can  drink  while  standing  on  the  head? 

Describe  the  gastric  juice. 

*  The  process  Is  what  is  known  as  a  reflex  action.    See  Chap.  XX. 


GASTRIC  DIGESTION.  157 

cus,  free  hydrochloric  acid  (about  .02  per  cent.),  and  a 
substance  called  pepsin,  which  in  acid  liquids  has  the  power 
of  converting  ordinary  proteids  into  closely  allied  bodies 
called  peptones.  It  also  dissolves  solid  proteids,  changing 
them  at  the  same  time  into  peptones. 

Peptones. — Ordinary  proteids  are  typical  examples  of 
what  are  called  "colloids;"  that  is  to  say,  substances  which 
do  not  readily  pass  through  moist  animal  membranes;  pep- 
tones are  a  kind  of  proteid  which  does  readily  pass  through 
such  membranes,  and  are,  therefore,  capable  of  absorption 
from  the  alimentary  canal.  (See  Dialysis,  p.  186.) 

Gastric  Digestion. — In  the  stomach  the  onward  progress 
of  the  food  is  stayed  for  some  time.  The  pyloric  sphincter 
remaining  contracted  closes  the  aperture  leading  into  the 
intestine,  and  the  irregularly  disposed  muscular  layers  of 
the  stomach  keep  its  semi-liquid  contents  in  constant 
movement,  by  which  all  portions  are  thoroughly  mixed 
with  the  secretion  of  its  glands.  In  the  stomach  part  of 
the  proteid  of  the  food  is  dissolved  and  turned  into  pep- 
tones. Certain  mineral  salts  (as  phosphate  of  lime,  of 
which  there  is  always  some  in  bread),  which  are  insoluble 
in  water  but  soluble  in  dilute  acids,  are  also  dissolved  in 
the  stomach.  On  the  other  hand,  the  gastric  juice  has  no 
action  upon  starch,  nor  does  it  digest  oily  substances.  By 
fche  solution  of  the  white  fibrous  connective  tissues  the 
.disintegration  of  animal  foodg,  commenced  by  the  teeth,  is 

Name  its  more  important  constituents.     What  powers  does  pepsin 


What  are  colloids?  Give  examples.  How  do  peptones  differ 
from  other  proteids? 

Does  food  pass  on  immediately  from  the  stomach  to  the  intestine? 
How  is  it  kept  back?  How  is  it  mixed  with  the  gastric  juice?  What 
happens  to  proteid  foods  in  the  stomach?  Name  another  substance 
dissolved  in  the  stomach.  Name  foodstuffs  which  are  not  changed 
in  the  stomach.  How  are  animal  foods  broken  up  in  the  stomach? 


158  THE  HUMAN  BODY. 

carried  mucli  further  in  the  stomach;  and  the  food-mass, 
mixed  with  much  gastric  secretion,  becomes  reduced  to  the 
consistency  of  a  thick  soup,  usually  of  a  grayish  color.  In 
this  state  it  is  called  chyme. 

The  Chyme  contains,  after  an  ordinary  meal,  a  consid- 
erable quantity  of  peptones,  which  are  in  great  part  gradually 
absorbed  into  the  blood  and  lymphatic  vessels  of  the  gastric 
mucous  membrane  and  carried  off,  along  with  other  dissolved 
and  dialyzable  bodies — for  example,  salts  and  sugar. 
After  the  food  has  remained  in  the  stomach  some  time  (one 
and  a  half  to  two  hours)  the  chyme  begins  to  be  passed 
on  into  the  intestine  in  successive  portions.  The  p}Tloric 
sphincter  relaxes  at  intervals,  and  the  rest  of  the  stomach, 
contracting  ut  the  same  moment,  injects  a  quantity  of 
chyme  into  the  duodenum;  this  is  repeated  frequently,  the 
larger  undigested  fragments  being  at  first  unable  to  pass  the 
orifice.  At  the  end  of  three  or  four  hours  after  an  ordinary 
meal  the  stomach  is  quite  emptied,  the  pyloric  sphincter 
finally  relaxing  to  such  an  extent  as  to  allow  any  larger  in- 
digestible masses,  which  the  gastric  juice  has  not  broken 
down,  to  be  squeezed  into  the  intestine.* 

The  Chyle, — When  the  chyme  passes  into  the  duodenum 
it  finds  preparation  made  for  it.  The  pancreas  commences 
to  secrete  as  soon  as  food  enters  the  stomach;  hence  a 
quantity  of  its  secretion  is  already  accumulated  in  the  intes- 
tine when  the  chyme  enters.  The  gall-bladder  is  distended 

What  is  chyme?  What  things  would  be  found  in  chyme  after 
an  ordinary  meal?  When  does  chyme  begin  to  be  sent  on  to  the  in- 
testine? How?  How  soon  is  the  stomach  completely  emptied  after  a 
meal?  What  has  accumulated  in  the  small  intestine  when  the  chyme 
reaches  it  ? 

*  Several  of  the  above  facts  were  first  observed  on  a  Canadian  trapper, 
Alexis  St.  Martin,  who  as  a  result  of  a  gunshot  wound  had  a  permanent  opening 
from  the  surface  of  the  abdomen  to  the  interior  of  the  stomach. 


THE  PANCREATIC  SECRETION.  159 

with  bile,  secreted  since  the  last  meal;  the  acid  chyme 
stimulating  the  duodenal  .mucous  membrane  causes, 
through  the  nervous  system,  a  contraction  of  the  muscular 
coat  of  the  gall-bladder,  and  so  a  gush  of  bile  is  poured  out 
on  the  chyme.  From  this  time  on  both  liver  and  pancreas 
continue  secreting  actively  for  some  hours,  and  pour  their 
products  into  tbo  intestine.  The  glands  of  Brunner  and 
the  crypts  of  Lieberkuhn  are  also  set  at  work.  All  of  these 
secretions  are  alkaline,  and  they  suffice  very  soon  to  more 
than  neutralize  the  acidity  of  the  gastric  juice,  and  so  to 
convert  the  acid  chyme  into  alkaline  chyle,  which,  as  found 
in  the  intestine  after  an  ordinary  meal,  contains  a  great  va- 
riety of  things:  water,  partly  swallowed  and  partly  derived 
from  the  salivary  and  other  secretions;  some  undigested 
proteids;  some  unchanged  starch;  oils  from  the  fats  eaten: 
peptones  formed  in  the  stomach  but  not  yet  absorbed;  sal- 
ines and  sugar,  which  have  also  escaped  complete  absorp- 
tion in  the  stomach;  indigestible  substances  taken  with  the 
food;  all  mixed  with  the  secretions  of  the  alimentary  canal. 
The  Pancreatic  Secretion  is  clear,  watery,  alkaline,  and 
much  like  saliva  in  appearance.  The  Germans  call  the 
pancreas  the  "abdominal  salivary  gland.  "  ^In  digestive 
properties,  however,  the  pancreatic  secretion  is  far  more 
important  than  the  saliva,  acting  not  only  on  starch  but 
on  proteids  and  fats.  On  starch  it  acts  like  the  saliva,  but 
more  energetically.  It  produces  changes  in  proteids  simi- 
lar to  those  effected  in  the  stomach,  but  by  the  agency  of  a 

How  is  an  outpouring  of  bile  on  the  chyme  brought  about  ?  Do 
liver  and  pancreas  cease  secreting  when  the  chyme  enters  the  intes- 
tine? What  other  glands  are  set  to  work?  How  is  the  acidity  of 
the  chyme  overcome?  What  is  chyle?  What  does  it  usually  con- 

• 


the  pancreatic  secretion.     What  foodstuffs  does  it  not 
it'    Describe  its  action  on  starch.    How  does  it  change  proteicte? 


160  THE  HUMAN  BODY. 

different  substance,  trypsin,  which  differs  from  pepsin  in 
acting  in  an  alkaline  instead  of  in  an  acid  medium.  On 
fats  it  has  a  double  action.  To  a  certain  extent  it  breaks 
them  up  into  fatty  acids  and  glycerine.*  The  fatty  acid 
then  combines  with  some  of  the  alkali  present  to  make 
a  soap,  which  being  soluble  in  water  is  capable  of  absorp- 
tion. f  Glycerine  also  is  soluble  in  water  and  capable 
of  absorption.  The  greater  part  of  the  fats  is  not,  how- 
ever, so  broken  up,  but  simply  mechanically  separated 
into  little  droplets  which  remain  suspended  in  the  chyle 
and  give  it  a  whitish  color;  just  as  cream-drops  are  sus- 
pended in  milk,  or  olive  oil  in  mayonnaise  sauce.  If  oil  bo 
shaken  up  with  water,  the  t\vo  cannot  be  got  to  mix;  immedi- 
ately the  shaking  ceases  the  oil  floats  up  to  the  top;  but  if 
some  raw  egg  be  added  a  creamy  mixture  is  readily  formed 
in  which  the  oil  remains  for  a  long  time  evenly  suspended 
in  the  watery  menstruum.  The  reason  of  this  is  that  each 
oil-droplet  becomes  surrounded  by  a  delicate  pellicle  of 
albumen,  and  is  thus  prevented  from  fusing  with  its  neigh- 
bors to  make  large  drops  which  would  soon  float  to  the  top. 
Such  a  mixture  is  called  an  emulsion,  and  the  albumen  of 
the  pancreatic  secretion  emulsifies  the  oils  in  the  chyle, 
which  becomes  white  (for  the  same  reason  as  milk  is  that 

How  does  trypsin  differ  from  pepsin  ?  How  does  pancreatic  secre- 
tion break  up  some  fats  ?  What  digestive  end  is  thus  attained  ? 
How  is  most  of  the  fat  eaten  acted  upon  by  the  pancreatic  secretion  ? 
Why  is  the  chyle  white  ?  How  may  we  mix  oil  with  water  ?  Ex- 
plain the  process.  What  is  an  emulsion  ?  What  emulsifies  the  oily 
matters  of  the  chyle  ? 


* 


=  3 


1  Stearin       +       3  Water    =    3  Stearic  acid    -f       1  Glycerine. 
t  Ordinary  soap  is  a  compound  of  a  fatty  acid  with  soda,  colored  and  scented 
by  the  addition  of  various  substances.    Soft  soap  is  a  compound  of  a  fat|;er    '-' 
with  potash.    Both  dissolve  in  water,  which  the  fats  from  which  thev.^" 
willi.otdo. 

f! 


THE  BILE.  161 

color)  because  the  innumerable  tiny  oil-drops  floating  in  it 
reflect  all  the  light  which  falls  on  its  surface. 

The  Bile, — Human  bile  when  quite  fresh  is  a  golden 
brown  liquid.  It  is  alkaline,  and  besides  coloring  matters, 
mineral  salts  and  water,  contains  the  sodium  salts  of  two 
nitrogenized  acids,  taurocholic  and  glycoclwlic,  the  former 
predominating  in  human  bile. 

The  Uses  of  Bile. — Bile  has  no  digestive  action  upon 
starch  or  proteids.  It  does  not  break  up  fats,  but  to  a 
limited  extent  emulsifies  them  when  shaken  up  with  them 
outside  the  body,  though  far  less  perfectly  than  the  pancre- 
atic secretion.  It  is  even  doubtful  if  this  action  is  exerted 
in  the  intestines  at  all.  In  many  animals,  as  in  man,  the  bile 
and  pancreatic  ducts  open  together  into  the  duodenum,  so 
that  on  killing  the  creature  during  digestion  and  finding 
emulsified  fats  in  the  chyle  it  is  impossible  to  say  whether 
or  not  the  bile  had  a  share  in  the  process.  In  the  rabbit, 
however,  the  pancreatic  duct  opens  into  the  intestine  about 
a  foot  farther  from  the  stomach  than  the  bile-duct,  and  it 
is  found  that  if  a  rabbit  be  killed  after  being  fed  with  oil, 
no  milky  chyle  is  found  down  to  the  point  where  the  pan- 
creatic duct  opens.  In  this  animal  therefore  the  bile  alone 
does  not  emulsify  fats,  and  since  the  bile  is  pretty  much 
the  same  in  rabbits  and  other  mammals  it  probably  does  not 
emulsify  fats  in  them  either.  From  the  inertness  of  bile 
with  respect  to  most  foodstuffs  it  has  been  doubted  if  it  is 
of  any  digestive  use  at  all,  and  whether  it  should  not  be 
regarded  merely  as  an  excretion,  poured  into  the  aliment- 
Describe  fresh  human  bile.  What  is  its  reaction?  Name  its 
chief  constituents. 

tfame   foods    on  which    bile  has  no  influence.     How  does   it 
acti  upon  fats  when  shaken  with  them?    Give  a  reason  for  doubt- 
it'  it  emulsifies  fats  ID  the  intestine. 


162  THE  HUMAN  BODY. 

ary  canal  to  be  got  rid  of.  But  there  are  many  reasons 
against  such  a  view.  In  the  first  place,  the  entry  of  the 
bile  into  the  upper  end  of  the  small  intestine,  where  it- 
has  to  traverse  a  course  of  more  than  twenty  feet  before 
getting  out  of  the  body,  makes  it  probable,  that  bile  has 
some  function  to  fulfill  in  the  intestine.  One  use  is 
no  doubt  to  assist  by  its  alkalinity  in  overcoming  the 
acidity  of  the  chyme,  and  so  to  allow  the  pancreatic  secre- 
tion to  act  upon  proteids.  Constipation  is  also  apt  to 
occur  in  cases  where  the  bile-duct  is  temporarily  stopped, 
so  that  the  bile  probably  helps  to  excite  the  contrac- 
tions of  the  muscular  coats  of  the  intestines;  and  it  is 
said  that  when  the  bile  secretion  is  deficient  putrefactive 
changes  are  extremely  apt  to  occur  in  the  intestinal  con- 
tents. Apart  from  such  secondary  actions,  however,  the 
bile  probably  has  some  influence  in  promoting  the  absorption 
of  fats.  If  one  end  of  a  very  narrow  glass  tube  moistened 
with  water  be  dipped  in  oil  the  latter  will  not  rise  in  it,  or 
but  a  short  way;  but  if  the  tube  be  moistened  with  bile 
instead  of  water  the  oil  will  ascend  higher.  Again,  oil 
passes  through  a  plug  of  porous  chij  kept  moist  with  bile, 
under  a  much  lower  pressure  than  through  one  wet  with 
water.  Hence  bile  by  moistening  the  cells  lining  the  intes- 
tine may  facilitate  the  passage  into  the  villi  of  oily  sub- 
stances. At  any  rate,  experiment  shows  that  if  the  bile  be 
prevented  from  entering  the  intestine  of  a  dog  the  animal 
eats  an  enormous  amount  of  food  compared  with  that 
amount  which  it  needed  previously;  and  that  of  this  food 

Give  reasons  for  believing  that  bile  is  not  a  mere  excretion.    How 
does  bile  aid  the  digestive  power  of  the  pancreas?     Point  out  other 
uses  of  bile.     Describe  experiments  which  tend   to  prove  t)~     ^  "-'° 
helps  in  promoting  the  absorption  of  fatty  mutters  from     ftct  2 
Uue.  * 


INTESTINAL  DIGESTION.  163 

a  great  proportion  of  the  fatty  part  passes  out  of  the  ali- 
mentary canal  unabsorbed.  There  is  no  doubt  therefore 
that  the  bile  somehow  aids  in  the  absorption  of  fats. 

The  Succus  Entericus  or  Intestinal  Juice  consists  of  the 
mixed  secretions  of  the  glands  of  Brunner  and  the  crypts 
of  Lieberkiihn.  It  is  very  difficult  to  obtain  it  pure,  and 
hence  its  digestive  action  is  but  imperfectly  known. 
It  is  alkaline  and  so  helps  to  overcome  the  acidity  of  the 
chyme  and  allow  the  trypsin  of  the  pancreas  to  act  on  pro- 
teids, and  seems  capable  itself  of  dissolving  some  kinds  of 
proteids  and  turning  them  into  peptones. 

Intestinal  Digestion. — Having  considered  separately  the 
digestive  actions  of  the  different  secretions  poured  into  the 
small  intestine,  we  may  now  consider  their  combined  ac- 
tion. The  acid  chyme  entering  the  duodenum  from  the 
stomach  is  more  than  neutralized  by  the  alkaline  secretions 
which  it  meets  in  the  small  intestine;  it  is  made  alkaline. 
This  alkalinity  allows  the  pancreatic  secretion  to  finish  the 
solution  and  transformation  into  peptone  of  proteids  which 
have  escaped  conversion  in  the  stomach.  The  pancreatic 
secretion  also  continues  that  conversion  of  insoluble  starch 
into  soluble  and  absorbable  grape  sugar,  which  had  com- 
menced in  the  mouth  but  was  checked  in  the  stomach. 
The  bile  and  pancreatic  secretion  together  emulsify  the 
fats,  with  which  they  are  thoroughly  mixed  by  the  contrac- 
tions of  the  muscular  coat  of  the  intestine;  they  get  them 
into  a  state  of  very  fine  division  in  the  form  of  microscopic 
droplets,  which  are  taken  up  by  the  cells  lining  the  intes- 
tine. To  a  certain  extent  the  fats  are  also  saponified.  The 

What  does  the  snccus  entericus  consist  of?    Why  is  its  digestive 
action  but  little  known?    Point  out  some  of  its  uses. 
Describe  the  process  of  intestinal  digestion. 


164  THE  HUMAN  BODY. 

result  of  all  these  processes  is  a  thin,  milky  looking  alka- 
line liquid  called  chyle. 

Indigestible  Substances.  —  With  every  meal  several 
things  are  eaten  which  are  not  digestible  at  all.  Among 
them  is  elastic  tissue,  forming  a  part  of  the  connective  tissue 
of  all  animal  foods,  and  cellulose,  which  is  the  chief  constit- 
uent of  the  cases  which  envelope  the  cells  of  plants.  The 
mucus  secreted  by  the  membrane  lining  the  alimentary 
tract  also  contains  an  indigestible  substance,  mucin.  These 
three  materials,  together  with  some  water,  some  undigested 
foodstuffs,  and  some  excretory  substances  found  in  the 
various  secretions  poured  into  the  alimentary  canal,  form 
a  residue  which  collects  in  the  lower  end  of  the  large 
intestine,  and  is  from  time  to  time  expelled  from  the 
body. 

Dyspepsia  is  the  common  name  of  a  variety  of  diseased 
conditions  attended  ./ith  loss  of  appetite  or  troublesome 
digestion.  Being  often  unattended  with  acute  pain,  and 
if  it  kills  at  all  doing  so  very  slowly,  it  is  pre-eminently 
suited  for  treatment  by  domestic  quackery.  In  reality, 
however,  the  immediate  cause  of  the  symptoms,  and  the 
treatment  called  for,  may  vary  widely;  and  the  detection 
of  the  cause  and  the  choice  of  the  proper  remedial  agents 
often  call  for  more  than  ordinary  medical  skill.  A  few  of 
the  more  common  forms  of  dyspepsia  may  be  mentioned 
here,  with  their  proximate  causes,  not  in  order  to  enable 
people  to  undertake  the  rash  experiment  of  dosing  them- 

Name  some  indigestible  substances  eaten  in  every  ordinary  meal. 
Point  out  the  source  of  each.  What  indigestible  substance  is  added 
in  the  alimentary  canal?  What  substances  are  found  in  the  lower 
end  of  the  large  intestine? 

What  is  meant  by  dyspepsia?  Why  is  it  not  a  wise  thing  for 
people  to  try  to  treat  it  themselves  without  skilled  advice? 


DYSPEPSIA.  165 

selves,  but  to  show  how  wide  a  chance  there  is  for  any 
unskilled  treatment  to  miss  its  end  and  do  more  harm 
than  good. 

Appetite  is  primarily  due  to  a  condition  of  the  mucous 
membrane  of  the  stomach,  which  in  health  comes  on  after 
a  short  fast  and  stimulates  its  'sensory  nerves  ;  and  loss  of 
appetite  may  be  due  to  any  of  several  causes.  The 
stomach  may  be  apathetic  and  lack  its  normal  sensibility 
so  that  the  empty  condition  does  not  act,  as  it  normally 
does,  as  a  sufficient  excitant.  When  food  is  taken  it  is  a 
further  stimulus  and  may  be  enough;  in  such  cases  "ap- 
petite comes  with  eating."  A  bitter  before  a  meal  is  useful 
as  an  appetizer  to  patients  of  this  sort.  On  the  other 
hand,  the  stomach  may  be  too  sensitive,  and  a  voracious 
appetite  be  felt  before  a  meal,  which  is  replaced  by  nausea, 
or  even  vomiting,  as  soon  as  a  few  mouthfuls  have  been 
swallowed  ;  the  extra  stimulus  of  the  food  then  over- 
stimulates  the  too  irritable  stomach,  just  as  a  draught 
of  mustard  and  warm  water  will  a  healthy  one.  The 
proper  treatment  in  such  cases  is  a  soothing  one.*  In 
states  of  "general  debility,  when  the  stomach  is  too  feeble 
to  secrete  under  any  stimulation,  the  administration  of 
weak  acids  and  artificially  prepared  pepsin  is  needed,  so  as 
to  supply  gastric  juice  from  outside  until  the  improved 

Describe  the  symptoms  of  some  chief  forms  of  dyspepsia. 

*  When  food  is  taken  it  ought  to  stimulate  the  sensory  gastric  nerves,  so  as 
to  excite  the  reflex  centres  for  the  secretory  nerves  and  for  the  dilatation  of 
the  blood-vessels  of  the  organ;  if  it  does  not,  the  gastric  juice  will  be  imper- 
fectly secreted.  In  such  cases  one  may  stimulate  the  secretory  nerves  by  weak 
alkalies  (p.  154),  as  apollinaris  water  or  a  little  carbonate  of  soda,  before 
meals;  or  give  drugs,  as  strychnine,  which  increase  the  irritability  of  reflex 
nerve-centres.  The  vascular  dilatation  may  be  helped  by  warm  drinks,  and  this 
is  probably  the  rationale  of  the  glass  of  hot  water  after  eating  which  has 
recently  been  in  vogue;  the  usual  cup  of  hot  coffee  after  dinner  is  a  more 
agreeable  form  of  the  same  aid  to  digestion. 


166  THE  HUMAN  BODY. 

digestion  strengthens  the  stomach  up  to  the  point  of  being 
able  to  do  its  own  work. 

Enough  has  probably  been  said  to  show  that  dyspepsia 
is  not  a  disease,  but  a  symptom  accompanying  many 
diseased  conditions,  requiring  special  knowledge  for  their 
treatment.  From  its  nature — depriving  the  body  of  its 
proper  nourishment — it  tends  to  intensify  itself,  and  so 
should  never  be  neglected ;  a  stitch  in  time  saves  nine. 

Absorption  from  the  Alimentary  Canal. — Through  its 
whole  extent  the  mucous  membrane  lining  the  digestive 
tube  is  traversed  by  very  closely  packed  tubes  of  two 
kinds,  the  blood  and  lymph  vessels.  Matters  ready  for 
absorption  pass  through  or  between  the  cells  covering  the 
surface  of  the  mucous  membrane,  and  then  through  the 
very  thin  walls  of  the  smallest  blood  and  lymph  vessels  ; 
and  by  these  vessels  are  conveyed  to  larger  channels  with 
thicker  walls,  which  all  ultimately  lead  to  the  heart.  From 
the  heart  the  digested  and  absorbed  food  is  distributed  to 
every  organ  of  the  body, 

Absorption  from  the  Mouth,  Pharynx,  and  Gullet  is  but 
slight.  Some  water,  some  common  salt,  some  sugar,  and 
some  grape  sugar  (made  from  starch  by  the  action  of  saliva) 
are  no  doubt  taken  up  during  the  processes  of  chewing  and 
swallowing.  But  the  time  which  elapses  between  taking  a 
mouthful  of  food  and  its  transference  to  the  stomach  is 
usually  too  short  to  allow  the  occurrence  of  any  consid- 
erable absorption. 

Why  should  dyspepsia  never  be  neglected? 

What  tubes  are  found  in  the  mucous  membrane  of  the  alimentary 
canal?  How  do  dissolved  foods  enter  them?  Where  are  the  ab- 
sorbed matters  carried?  To  what  parts  are  they  finally  distributed? 

What  foodstuffs  are  partly  absorbed  in  mouth,  pharynx,  and 
gullet?  Why  does  not  any  great  amount  of  absorption  take  place 
in  those  parts? 


PLATE     III.  — A     GENERAL     VIEW     OF     THE     LYMPHATICS     OR     ABSORBENTS.        That     portion      of      tilt 

known  as  the  lacteals  is  seen  at  d,  passing  from  the  small  intestine  e  to  the  thoracic  duct  /. 


EXPLANATION   OF    PLATE  TIL 

A  GENERAL  VIEW  OF  THE  LYMPHATIC  OR  ABSORBENT  SYSTEM 

OP  VESSELS. 

e,  A  portion  of  the  small  intestine  from  which  lacteals  or  chyle- 
conveying  vessels,  d,  proceed,  their  origin  within  the  villi  may  be 
seen  magnified  in  fig.  51;  /,  the  duct  called  thoracic,  into  which  the 
lacteals  open.  This  duct  passes  up  the  hack  of  the  chest,  and  opens 
into  the  great  veins  at  g,  on  the  left  side  of  the  neck :  here  the  chyle 
mingles  with  the  venous  blooA  In  the  right  upper,  and  lower  limbs 
the  superficial  lymphatic  vessels  1 1 1 1,  which  lie  beneath  the  skin, 
are  represented.  In  the  left  upper  and  lower  limbs  the  deep  lym- 
phatic vessels  which  accompany  the  deep  blood-vessels  are  shown. 
The  lymphatic  vessels  of  the  lower  limbs  join  the  thoracic  duct  at  the 
spot  where  the  lacteals  open  into  it:  those  from  the  left  upper  limb 
and  from  the  left  side  of  the  head  and  neck  open  into  that  duct  at 
the  root  of  the  neck.  The  lymphatics  from  the  right  upper  limb  and 
from  the  right  side  of  the  head  and  neck  join  the  great  veins  at  n. 
m  m,  enlargements  called  lymphatic  glands,  situated  in  the  course  of 
the  lymphatic  vessels.  These  vessels  convey  a  fluid  called  lymph,, 
which  mingles  with  the  blood  in  the  great  veins.  A  fuller  account  of 
the  lymphatic  vessels  in  general,  as  distinguished  from  that  section  of 
them  known  as  the  lacteals,  will  be  found  on  p.  188. 


ABSORPTION  FROM  THE  STOMACH.  167 

Absorption  from  the  Stomach  is  more  important.  Food 
stays  there  a  considerable  time,  and  a  good  deal  of  the 
substances  mentioned  above  as  being  absorbed  to  a  slight 
degree  on  their  way  to  the  stomach,  are  taken  up  to  a 
much  greater  extent  by  the  mucous  membrane  of  the 
stomach  itself  and  passed  on  into  the  general  blood  current. 
In  addition,  a  large  proportion  of  albuminous  food  is 
turned  in  the  stomach  into  peptones,  which  can  be  and 
are  readily  absorbed  by  the  vessels  of  the  gastric  mucous 
membrane. 

Absorption  from  the  Small  Intestine  is  by  far  the  most 
important  in  bringing  nutritive  matters  into  the  body. 
The  stomach  is  an  organ  rather  of  digestion  than  absorp- 
tion; the  small  intestine,  on  the  other  hand,  is  specially 
constructed  to  absorb.  Its  valvulae  conniventes  delay  the 
progress  of  the  food  mass  which  stagnates  in  the  hollows 
between  them;  and  its  innumerable  villi,  with  their  blood- 
vessels and  lymphatics  (p.  147),  reach  out,  like  so  many 
rootlets,  into  the  chyle  and  take  it  up. 

The  sugars  reaching  the  small  intestine  or  formed  in  it 
are  absorbed  mainly  by  the  blood-vessels  and  carried  to  the 
liver,  where  they  are  turned  into  glycogen  (p.  151),  which  is 
heaped  up  in  the  liver  during  digestion,  and  slowly  given 
out  to  the  blood,  as  its  sugar  is  used  up  gradually  before 
the  next  meal.  The  peptones  passed  into  the  intes- 
tine from  the  stomach,  or  formed  in  it  by  the  action  of  the 

Why  does  more  absorption  take  place  from  the  stomach?  Name 
things  absorbed  from  both  mouth  and  stomach?  What  food  matters 
are  first  absorbed  from  the  stomach? 

Where  does  the  most  important  food  absorption  occur?  What 
structural  peculiarities  of  the  small  intestine  peculiarly  fit  it  for  ab- 
sorbing? 

What  vessels  absorb  sugars  in  the  small  intestine?  To  what  organ 
are  these  sugars  conveyed?  What  there  becomes  of  them? 


168  THE  HUMAN  BODY. 

pancreatic  secretion,  are  partly  taken  up  by  its  lymphatics 
and  partly  by  its  blood-vessels.  The  emulsified  fats  main- 
ly pass  into  the  lymphatics  of  the  villi,  and  are  carried  off 
by  them. 

The  Lacteals. — The  innumerable  tiny  fat  drops  drained 
off  by  the  intestinal  lymphatics  or  lacteals  after  an 
ordinary  meal  make  their  contents  look  white  and  milky, 
hence  the  name.*  During  fasting  the  lymphatics  of  the 
small  intestine,  like  those  in  other  parts  of  the  body  (see 
Chap.  XIII.)  convey  a  clear  colorless  liquid. 

Absorption  from  the  Large  Intestine. — In  the  duo- 
denum the  bulk  of  food  entering  from  the  stomach  is 
increased  by  the  bile  and  pancreatic  secretions  poured  out 
on  it.  Thenceforth  absorption  overbalances  excretion,  and 
the  food-mass  becomes  less  and  less  in  bulk  to  the  lower 
end  of  the  ileum.  The  contractions  of  the  small  intestine 
drive  on  its  continually  diminishing  contents,  until  they 
reach  the  ileo-colic  valve,  through  which  they  are  ulti- 
mately pressed.  When  the  mass  enters  the  large  intestine 
its  nutritive  portions  have  been  almost  entirely  absorbed, 
and  it  consists  chiefly  of  some  water,  with  the  indigestible 
portions  of  the  food  and  of  the  secretions  of  the  alimentary 
canal.  It  contains  cellulose,  elastic  tissue,  mucin,  and 
somewhat  altered  bile  pigments;  commonly  some  fat  if  a 
large  quantity  has  been  eaten;  and  some  starch,  if  raw  veg- 

How  are  emulsified  fats  carried  off? 

What  are  the  lacteals?  Why  so  called?  Under  what  conditions 
do  the  lacteals  not  contain  milky  looking  chyle? 

In  what  part  of  the  alimentary  canal  does  absorption  more  than 
balance  the  amount  of  liquid  poured  out  on  the  food? 

What  are  the  constituents  of  the  mass  passing  from  the  small  into 
the  large  intestine?  What  changes  does  this  mass  undergo  as  it 
passes  along  the  large  intestine? 

*  From  Latin,  lac,  milk. 


APPENDIX.  169 

etables  have  formed  part  of  the  diet.  In  its  progress 
through  the  large  intestine  the  food-mass  loses  still  more 
water,  and  the  digestion  of  starch  and  the  absorption  of 
fats  is  continued.  Finally  the  residue,  with  some  excre- 
tory matters  added  to  it  in  the  large  intestine,  is  expelled 
from  the  body. 


APPENDIX  TO  CHAPTER  XII. 

The  digestion  and  absorption  of  food  are  such  fundamental  facts 
in  physiology  that  a  thoroughly  intelligent  comprehension  of  them  is 
of  great  importance;  at  the  same  time  they  are  so  largely  merely 
chemico-physical  phenomena  that  they  are  readily  ilhistrated  by  a 
few  simple  experiments.  These  described  below  take  but  little  time 
and  cost  but  little  money,  while  they  cannot  fail  to  be  of  value  not 
merely  in  interesting  a  class,  but  in  giving  its  members  a  much  better 
idea  of  the  way  in  which  food  is  digested  than  they  can  -get  from 
merely  reading  a  book. 

1.  Anatomy  of  the  Alimentary  Canal. — Kill  a  rat  by  chloroform  or 
drowning.  Dissect  away  the  skin  from  the  whole  ventral  aspect  of 
the  body. 

Note  in  the  neck  region  the  large  salivary  glands  which  meet  in  the 
middle  line:  the  posterior  gland,  close  to  the  middle  line,  rounded 
and  compact,  is  the  submaxillary;  on  raising  it,  its  duct  will  be  seen 
passing  forwards  to  the  mouth,  into  which  it  may  be  followed  by 
separating  the  halves  of  the  lower  jaw. 

The  large  gland,  composed  of  several  loosely  united  lobes,  and 
reaching  from  the  neighborhood  of  the  ear  to  the  submnxillary,  is  the 
parotid.  Its  duct  will  be  found  passing  forwards  over  the  face  to 
the  mouth,  near  the  angle  of  which  it  passes  in  through  the  cheek 
muscles. 

In  front  of  the  submaxillary  will  be  found  a  small  gland,  the  sub- 
lingual. 

Remove  the  muscles,  etc.,  covering  the  larynx  and  trachea;  cut 
away  the  front  and  side  walls  of  tl.e  chest  and  abdomen;  remove 
larynx,  trachea,  lungs,  and  heart. 

The  gullet,  a  slender  muscular  tube,  will  now  be  exposed  in  the 
neck;  trace  it  through  the  chest;  note  the  relative  positions  of  the 
abdominal  viscera  as  now  exposed,  before  displacing  any  of  them; 
then  turning  the  liver  up  out  of  the  way,  follow  the  gullet  in  the 
abdomen  until  it  ends  in  the  stomach. 


170  THE  HUMAN  BODY. 

Note  the  form  of  the  latter  organ ;  its  projection  (fundus)  to  the 
left  of  the  entry  of  the  gullet;  its  great  and  small  curvatures;  its 
narrower  pyloric  portion  on  the  right,  from  which  the  small  intestine 
proceeds.  Attached  to  the  stomach,  and  hanging  down  over  the  other 
abdominal  viscera,  notice  a  thin  membrane,  the  amentum. 

Follow  and  unravel  the  coils  of  the  small  intestine,  spreading  out 
as  far  as  possible  the  delicate  membrane  (mesentery)  which  slings  it. 
In  the  mesentery  are  numerous  bands  of  fat,  running  in  which  will 
be  seen  blood-vessels  and  lacteals. 

The  termination  of  the  small  intestine  by  opening  into  the  side  of 
the  large.  Observe  the  caecum  or  blind  end  of  the  latter,  projecting 
on  one  side  of  the  point  of  entry  of  the  small  intestine;  on  the  other 
side  follow  the  large  intestine  until  it  ends  at  the  anal  aperture,  cut- 
ting away  the  front  of  the  pelvis  to  follow  its  terminal  portion  (rec- 
tum). The  portion  between  the  caecum  and  the  rectum  is  the  colon. 

Spread  out  the  portion  of  the  mesentery  lying  in  the  concavity  of 
the  first  coil  (duodenum)  of  the  small  intestine;  in  it  will  be  seen  a 
thin  branched  glandular  mass,  the  pancreas. 

Observe  the  portal  vein  entering  the  under  side  of  the  liver  by 
several  branches.  Alongside  it  will  be  seen  the  gall-duct,  formed  by 
the  union  of  two  main  branches,  and  proceeding,  as  a  slender  tube, 
to  open  into  the  duodenum  about  an  inch  and  a  half  from  the  pyloric 
orifice  of  the  stomach. 

Note  the  spleen:  an  elongated  red  body  lying  in  the  mesentery, 
behind  and  to  the  left  of  the  stomach. 

Divide  the  gullet  at  the  top  of  the  neck,  and  the  rectum  close  to 
the  anus,  and  severing  mesenteric  bands,  etc.,  by  which  intermediate 
portions  of  the  alimentary  canal  are  fixed,  remove  the  whole  tube; 
then  cutting  away  the  mesentery,  spread  it  out  at  full  length,  and 
note  the  relative  length  and  diameter  of  its  various  parts.  The  whole 
is  seven  or  eight  times  as  long  as  the  head  and  trunk  of  the  animal, 
and  the  small  intestine  forms  by  far  the  longest  part  of  it. 

Open  the  stomach ;  note  that  the  mucous  membrane  lining  the  fun- 
dus is  thin  and  smooth,  and  is  sharply  marked  off  from  the  thick 
corrugated  mucous  membrane  lining  the  rest  of  the  organ.  (This  is 
not  the  case  in  the  human  stomach.)  Pass  probes  through  the  car- 
diac orifice  into  the  gullet  and  through  the  pyloric  orifice  into  the 
duodenum. 

Remove  the  liver;  note  its  general  form. 

Obtain  from  your  butcher  an  inch  or  two  of  the  small  intestine 
of  a  recently  killed  calf.  Place  in  50  per  cent,  alcohol  for  twenty- 
four  hours.  Then  open  under  water  and  examine  with  a  hand  lens  to 
see  the  villi, 


APPENDIX.  171 

2.  The  Action   of  Saliva  on   Starch. — Make  a  thin  paste  of  good 
arrowroot  (which  is  almost  pure  starch)  with  boiling  water.     Let  it 
cool. 

a.  Add  two  or  three  drops  of  this  starch  paste  to  half  a  test  tube- 
ful  of  cold  water;  next  add  three  or  four  drops  of  solution  of  caustic 
potash  and  two  or  three  drops  of  dilute  watery  solution  of  blue  vitriol 
(cupric  sulphate).     Mix  thoroughly  and  boil  over  a  spirit  lamp.     No 
orange-red  precipitate  will  result.    This  shows  that  there  is  no  grape 
sugar  in  the  starch  paste. 

b.  Rinse  the  mouth  thoroughly  and  then  collect  a  small  quantity  of 
saliva  in  a  test  tube.     Dilute  with  water.     Add  caustic  potash  and 
cupric  sulphate  solutions  as  above;  mix  thoroughly  and  boil.     The 
mixture  will  become  violet,  but  give  no  orange-red  precipitate;  there- 
fore there  is  no  grape  sugar  in  saliva. 

c.  Take  now  three  drops  of  the  starch  paste  and  a  teaspoonful  of 
saliva;  mix  with  a  half  test  tubeful  of  water.     Place  the  mixture  in 
a  moderately  warm  place  for  five  minutes.     Then  add  a  few  drops  of 
the  caustic  potash  and  cupric  sulphate  solutions;  mix  and  boil.     An 
abundant  orange  or  brick -red  precipitate  will  be  thrown  down,  prov- 
ing the  presence  of  grape  sugar,  which  has  been  produced  by  the 
action  of  the  saliva  on  the  starch. 

3.  Gastric   Digestion. — a.  Obtain  a  pig's  stomach.     Cut  it   open 
and  wash  away  its  contents  with  a  gentle  stream  of  water.     Then 
dissect  off  the  mucous  membrane  from  its  middle  part,  mince  and 
put  aside  for  a  couple  of  days  in  three  or  four  ounces  of  glycerine. 
The  glycerine  dissolves  the  pepsin.     Then  strain  off  the  glycerine 
through  muslin. 

b.  Get  a  butcher  to  "  whip"  some  fresh  drawn  blood  for  you  with 
a  bunch  of  wire  or  twigs.     The  blood  fibrin  will  collect  on  these 
(p.  181),  and  when  thoroughly  washed  with  water, forms  a  good  proteid 
for  digestion  experiments.     One  lot  of  it  thus  obtained  and  washed 
may  be  put  aside  in  50  per  cent,  alcohol,  and  will  provide  material  for 
digestion  experiments  for  years. 

c.  Add  a  teaspoonful  of  muriatic  acid  to  a  pint  of  water. 

d.  Dilute  a  teaspoonful  of  the  pepsin  solution  a  with  two  table- 
spoonfuls  of  water.     Fill  a  test  tube  with  the  mixture;  add  a  few 
shreds  of  washed  fibrin,  and  set  aside  in  a  warm  but  not  hot  place  for 
twenty-four  hours.   No  change  will  occur,  showing  that  pepsin  alone 
will  not  dissolve  proteid s. 

e.  Put  some  shreds  of  fibrin  in  a  test  tube  of  the  mixture  c  in  a 
warm  place  for  twenty-four  hours.     The  fibrin  will  swell  up  and 
become  translucent,  but  will  not  dissolve.     This  shows  that  dilute 
acids  will  not  in  a  short  time  dissolve  proteids. 


172  THE  HUMAN  BODY, 

f.  Half  fill  a  test  tube  with  the  mixture  c,  add  a  teaspoonful  of 
the  pepsin  solution  a,  and  then  a  few  shreds  of  fibrin.  Place  in  a 
warm  place  for  twenty-four  hours.  The  fibrin  will  be  more  or  less 
completely  dissolved  at  the  end  of  that  time.  We  thus  find  that 
pepsin  alone  and  dilute  acid  alone  (at  least  in  a  moderate  time)  will 
not  dissolve  proteids,  but  that  acting  together  they  quickly  effect  a 
solution. 

4.  The  Action   of  Bile   on  Fatty  Substances. — a.   Shake  up  some 
olive  oil  with  water  in  a  test  tube.     The  two  liquids  soon  separate 
when  the  shaking  ceases. 

b.  Obtain  an  ox  gall  from  the  butcher.  Cut  it  open  and  collect 
the  bile.  (The  bile  of  herbivorous  animals  differs  from  human  bile 
in  being  green  in  color.)  Shake  up  some  oil  with  bile  instead  of 
water.  A  creamy  emulsion  is  formed  from  which  the  oil  only  slowly 
floats  up  to  the  top. 

5.  The  Action  of  the  Pancreatic   Secretion   on  Fats. — a.    Obtain 
a  pig's  pancreas;  mince,  and  extract  with  about  its  own  bulk  of  water 
for  two  or  three  hours.     Strain  off  the  watery  infusion.     Add  to  it 
half  its  bulk  of  oil  in  a  test  tube  and  shake  thoroughly.    The  oil  will 
be  very  thoroughly  emulsified ;  and  separate  very  slowly  on  standing. 

6.  Action   of  Pancreatic   Secretion   on   Starch. — With  some  of  the 
watery  extract  of  pancreas  perform  the  experiments  described  above 
under  heading  2;  substituting  pancreatic  extract  for  saliva. 

7.  Action  of  Pancreatic  Secretion  on  Proteids. — a.   Obtain  a  fresh 
pig's  pancreas.     Lay  aside  in  a  cool  place  for  twenty-four  hours, 
Mince,  and  extract  for  two  days  with  twice  its  bulk  of  glycerine. 
Strain  off  the  glycerine  extract. 

b.  Dilute  the  glycerine  extract  with  ten  times  its  bulk  of  water. 
Place  part  of  this  mixture  in  a  test  tube  together  with  some  fibrin 
shreds,  and  put  aside  in  a  warm  place.     After  twenty-four  hours 
none  of  the  fibrin  will  have  been  dissolved. 

c.  To  the  diluted  glycerine  extract  as  above  add  a  teaspoonful  of 
dilute  acid  (3  c).     The  fibrin  will  swell  but  not  dissolve. 

d.  To  another  portion  of  the  diluted  glycerine  extract  add  just 
sufficient  bicarbonate  of  soda  to  make  it  distinctly  alkaline,  as  tested 
by  litmus  paper.     Then  put  in  some  fibrin  and  set  aside  in  a  warm 
place  fpr  a  day.   The  fibrin  will  be  more  or  less  completely  dissolved. 
We  thus  find  that  the  pancreas  affords  a  substance  which,  in  the 
presence  of  weak  alkalies, dissolves  proteids. 

The  fat-absorbing  power  of  the  lymphatics  of  the  small  intestine 
is  very  readily  demonstrable,  without  giving  pain  to  an  animal  or  any 
unnecessary  destruction  of  life.  In  most  families  superfluous  kittens 
or  puppies  have  to  be  killed  at  the  time  of  birth.  Feed  a  kitten  or 


APPENDIX.  173 

puppy  on  rich. milk,  and  three  hours  after  place  it  in  a  box  or  under  a 
bell-jar  with  a  sponge  soaked  with  ether  or  chloroform.  When  the 
animal  is  completely  insensible  cut  off  its  head,  and  then  rapidly  open 
the  abdomen  and  spread  out  the  mesentery  (the  thin  membrane  which 
slings  the  small  intestine).  In  it  will  be  seen  a  beautiful  network  of 
lacteal  vessels  filled  with  milk-white  liquid,  some  of  which  can  be 
collected  if  one  of  the  lacteals  be  cut  open.  For  comparison  a  kitten 
or  puppy  may  be  used  which  has  had  no  food  for  eight  or  ten  hours. 
The  lacteals  being  then  filled  with  clear,  watery -looking  lymph,  will 
be  recognized  with  difficulty. 


CHAPTEP   XIII. 
BLOOD  AND  LYMPH, 

Why  we  need  Biood. — Some  very  small  animals  of  simple 
structure  require  no  blood;  every  part  catches  its  own  food 
and  gives  off  its  own  wastes  to  the  air  or  water  in  which 
the  creature  lives.  When,  however,  an  animal  is  larger  and 
more  complex,  made  up  of  many  organs,  some  of  which  are 
far  away  from,  the  surface  of  its  body,  this  is  impossible; 
some  organs  are  therefore  set  apart  to  catch  food,  and 
arrangements  made  to  carry  some  of  this  food  to  the  others. 
In  our  own  bodies  many  parts  lie  faraway  from  the  stomach 
and  intestines  which  receive,  digest,  and  absorb  our  food, 
and  from  the  lungs  which  take  oxygen  gas  out  of  the  air 
we  breathe;  yet  every  part,  bone  and  muscle,  brain  and 
nerve,  skin  and  gland,  needs  a  steady  supply  of  both  of  these 
things  to  keep  it  alive.  The  division  of  labor,  in  accordance 
with  which  some  organs  are  especially  set  apart  for  the 
purpose  of  receiving  substances  from  the  outside  world 
to  build  up,  nourish,  and  repair  the  body,  necessitates 
an  arrangement  by  which  the  matters  received  shall  be 
distributed  to  other  parts.  This  distribution  is  accomplished 
by  the  blood,  which  flows  into  every  organ  from  the  crown 
of  the  head  to  the  sole  of  the  foot.  Being  pumped  round 

What  kind  of  animals  do  not  need  blood?  How  are  their  want* 
supplied  and  their  wastes  removed?  Why  do  we  find  special  recep- 
tive organs  in  larger  animals?  Illustrate  from  the  human  body,, 
What  arrangement  is  necessitated  by  the  fact  that  special  organs  are 
set  apart  in  the  body  for  receiving  food  and  oxygen?  How  is  the 
distribution  effected? 

[174] 


''THE  BLOOD.  175 


and  round,  from  place  to  place,  by  the  heart,  the  blood  picks 
up  nourishing  things  in  its  course  through  the  walls  of 
the  alimentary  canal,  and  oxygen  as  it  flows  through  the 
lungs;  it  then  carries  them  to  all  other  parts  of  the  body. 

The  Removal  of  Wastes. — The  rapidly  flowing  blood  not 
only  conveys  a  supply  of  nutritive  material  for  all  the 
organs,  but  is  a  sort  of  sewage  stream  that  drains  off  their 
wastes  (p.  108),  and  carries  them  to  the  excretory  organs,  by 
which  they  are  sent  entirely  out  of  the  body. 

The  blood  is  a  middleman:  on  the  one  hand,  between  the 
receiving  organs  (lungs  and  alimentary  canal)  and  all  the 
rest;  and  on  the  other  hand,  between  the  excretory  organs 
and  all  the  others.  Each  part  is  thus  'kept  in  a  well-fed 
and  healthy  state,  though  it  may  lie  far  distant  from  all 
places  where  new  materials  first  enter  the  body,  and  from 
those  where  refuse  and  deleterious  substances  are  finally 
passed  from  it. 

The  Blood,  as  every  one  knows,  is  a  red  liquid  which  is 
yery  widely  distributed  over  the  body,  since  it  flows  from 
any  part  of  the  surface  when  the  skin  is  cut  through. 
There  are  very  few  portions  of  the  body  into  which  blood 
is  not  carried.  One  of  them  is  the  outer  layer  of  the  skin;* 
hairs  and  nails,  the  hard  parts  of  the  teeth  and  most  carti- 
lages also  contain  no  blood;  these  non-vascular  tissues  are 

Where  does  the  blood  receive  nutritive  matters?  Oxygen? 
What  does  it  do  with  them? 

What  part  does  the  blood  play  in  the  removal  of  wastes? 

State  briefly  the  functions  of  the  blood  with  reference  to  the 
nutritive  processes  of  the  body 

What  is  blood?  How  do  we  know  that  it  is  widely  distributed? 
Name  parts  into  which  blood  does  not  flow.  How  are  the  non- vas- 
cular tissues  nourished? 

*  The  absence  of  blood  in  the  superficial  layer  of  the  skin  may  be  readily 
shown:  take  a  fine  needle  threaded  with  silk;  by  taking  shallow  stitches  a  pat- 
tern can  be  easily  embroidered  on  the  palm  or  back  of  the  hand  without  draw 
ing  a  drop  of  blood, 


ire 


THE  HUMAN  BODY. 


nourished   by   liquid   which   soaks   through   the   wulis  of 
blood-vessels  in  neighboring  parts. 

The  Histology  of  Blood. — Fresh  blood  is  to  the  unassisted 
eye  a  red  opaque  liquid  showing  no  sign  of  being  made  up 
of  different  parts;  but  when  examined  by  a  microscope  it  is 


FIG.  53  —Blood-corpuscles.  A,  magnified  about  400  diameters.  The  red 
corpuscles  have  arranged  themselves  in  rouleaux;  a.a,  colorless  corpuscles; 
B,  red  corpuscles  more  magnified  and  seen  in  focus;  E,  a  red  corpuscle  slightly 
out  of  focus.  Near  the  right-hand  top  corner  is  a  red  corpuscle  seen  in  three- 
quarter  face,  and  at  C  one  seen  edgewise.  f,G,H,I,  white  corpuscles  highly 
magnified. 

seen  to  consist  of  a  liquid,  the  'blood-plasma,  which  has 
floating  in  it  countless  multitudes  of  closely  crowded  and 
extremely  minute  solid  bodies  known  as  blood-corpuscles* 
The  liquid  is  colorless  and  watery-looking;  the  corpuscles 
are  of  two  kinds,  red  and  colorless.  The  red  corpuscles  are 

Describe  the  appearance  of  fresh  drawn  blood.  What  is  seen 
when  a  drop  is  examined  with  a  microscope?  Describe  the  blood- 
plasma.  Name  the  kinds  of  blood-corpuscles. 


THE  RED   CORPUSCLES  OF  OTHER  ANIMALS.     177 

by  far  the  most  numerous  and  give  the  blood  its  color;  they 
arc  so  tiny  and  so  plentiful  that  about  five  millions  of  them 
are  contained  in  one  small  drop  of  blood.  They  are  so 
closely  packed  that  the  unaided  eye  cannot  see  the  spaces 
between  them,  and  so  the  whole  blood  appears  uniformly 
red. 

The  Red  Corpuscles  of  Human  Blood  (Fig.  53)  are  cir- 
cular disks  a  little  hollowed  out  on  each  face!  Seen  singly 
with  a  microscope  each  is  not  red  but  pale  yellow;  it  is 
only  when  they  are  crowded  in  a  heap  that  the  mass  looks 
red;  a  drop  of  blood  spread  out  very  thin  on  glass,  or  mixed 
with  a  tablespoonful  of  water,  is  pale  yellow  and  not  red. 
Soon  after  blood  is  drawn  most  of  the  red  corpuscles  cohere 
side  by  side  in  rows,  something  like  piles  of  coin. 

The  Red  Corpuscles  of  other  Animals. — The  red  corpus- 
cles of  most  mammalia  resemble  those  of  man  in  being 
circular  biconcave  pale  yel- 
low disks;  those  of  camels 
and  dromedaries,  however, 
are  oval.  The  blood-cor- 
puscles of  dogs  are  so 
like  those  of  man  in  size 
that  they  cannot  be  FlG- ^-Red  corpuscles  of  the  Frog. 

readily  distinguished;  but  in  most  cases  the  size  is  suffi- 
ciently different  to  enable  a  safe  opinion  to  be  formed.  This 

Which  kind  is  most  numerous?  Give  some  idea  of  their  num- 
ber. Why  does  the  blood  look  uniformly  red  to  the  unaided  eye? 

Describe  the  form  of  human  red  blood-corpuscles.  What  is 
the  color  of  one  seen  by  itself  with  a  microscope?  How  may  we 
show  that  blood  looks  red  only  when  its  corpuscles  are  crowded  close 
together?  How  do  the  red  corpuscles  become  arranged  soon  after 
blood  is  drawn  ? 

Describe  the  corpuscles  of  most  mammalia.  How  do  those  of 
camels  and  dromedaries  differ  from  the  corpuscles  of  other  mam- 
mals? Why  cannot  a  d'>g's  blood  be  easily  distinguished  from 
human  blood? 


178  THE  HUMAN  BODY. 

fact  has  often  been  used  to  further  the  ends  of  justice  in 
determining  whether  spots  of  blood  on  the  clothes  of  a 
suspected  murderer  were  really  due  to  the  cause  assigned 
by  him.  The  red  blood-corpuscles  of  birds,  reptiles,  amphi- 
bians, and  fishes  cannot  be  confounded  with  those  of  man, 
since  they  are  oval  and  contain  a  nucleus  in  the  centre  such 
as  is  not  found  in  our  red  corpuscles. 

Haemoglobin. — Each  red  corpuscle  is  soft  and  jelly  like. 
Its  chief  constituent,  besides  water,  is  a  substance  called 
licem' -o-glof -bin,  which  has  the  power  of  combining  with 
oxygen  when  in  a  place  where  that  gas  is  plentiful,  and  of 
giving  it  off  again  in  a  region  where  oxygen  is  absent  or 
present  only  in  small  quantity.  Hence  as  the  blood  flows 
through  the  lungs,  which  are  constantly  supplied  with  fresh 
air,  its  corpuscles  take  up  oxygen,  which,  as  it  flows  on,  is 
carried  by  them  to  distant  parts  of  the  body  where  oxygen 
is  deficient,  and  there  given  up  to  the  tissues.  This  oxygen- 
carrying  is  the  function  of  the  red  corpuscles. 

Arterial  and  Venous  Blood. — Haemoglobin  itself  is  dark 
purplish-red  in  color;  haemoglobin  combined  with  oxygen 
is  bright  scarlet  red.  Accordingly,  the  blood  which  flows  to 
the  lungs  after  giving  up  its  oxygen  is  dark  red  in  color, 
and  that  which,  having  got  a  fresh  supply  of  oxygen,  flows 
away  from  the  lungs  is  bright  scarlet.  The  bright  red  blood 
is  called  arterial  and  the  dark  red  venous. 

Can  the  blood  of  most  mammals  be  certainly  distinguished  from 
human  blood  ?  Point  out  a  use  which  has  been  made  of  this  fact.  How 
do  the  red  corpuscles  of  birds,  reptiles,  and  fishes  differ  from  human? 

Describe  the  consistence  of  a  red  corpuscle.  What  are  its  chief 
constituents?  Point  out  an  important  property  of  haemoglobin.  How 
does  this  enable  it  to  receive  and  distribute  oxygen?  What  is  the 
function  of  the  red  corpuscles? 

What  is  the  color  of  haemoglobin?  What  of  haemoglobin  com- 
bined with  oxygen?  What  is  the  color  of  blood  flowing  to  the 
lungs?  Why?  The  color  of  that  flowing  from  the  lungs?  Why? 
What  is  arterial  blood?  What  venous? 


THE  COAGULATION  OF  BLOOD. 


179 


The  Colorless  Blood  Corpuscles  are  a  little  larger  than 
the  red,  but  much  less  numerous  (about  1  to  300).  As 
their  name  implies  they  contain  no  coloring  matter.  Each 
is  a  cell  with  a  nucleus,  and  has  the  wonderful  property  of 
being  able  to  change  its  own  shape.  Watched,  with  a  micro- 
scope the  corpuscle  may  be  seen  to  alter  its  form  slowly 
(Fig.  55),  or  even  to  creep  across  the  glass.  These  corpus- 
cles are  thus  little,  independently 
moving  cells  which  live  in  our  blood. 
The  pus  or  "  matter"  which  collects 
in  an  abscess  is  chiefly  made  up  of 
colorless  blood  -  corpuscles  which 
have  bored  through  the  walls  of 
the  smallest  blood-vessels.  Their 
movements  are  very  like  those  of  the 
microscopic  animal  named  amw'ba, 
and  are  accordingly  called  amoeboid. 

The  Coagulation  of  Blood. — When  blood  is  first  drawn 
from  the  living  body  it  is  perfectly  liquid,  flowing  in  any 
direction  as  readily  as  water.  This  condition  is  only  tem- 
porary; in  a  few  minutes  the  blood  becomes  viscid  and  sticky, 
and  comes  to  resemble  a  thick  red  syrup;  the  viscidity  be- 
comes more  and  more  marked,  until,  after  the  lapse  of  five 
or  six  minutes,  the  whole  mass  sets  into  a  jelly  which  ad- 
heres to  the  vessel  containing  it,  so  that  this  may  be  in- 
verted without  any  blood  whatever  being  spilled.  This 
stage  is  known  as  that  of  gelatinization,  and  is  also  not  per- 

How  do  the  colorless  corpuscles  differ  from  the  red  in  size  and 
number?  What  is  each?  What  property  does  it  possess?  What  is 
seen  when  one  is  watched  with  the  help  of  a  microscope?  What  is 
pus?  Why  are  the  movements  of  the  colorless  corpuscles  called 
amoeboid? 

What  is  the  consistency  of  fresh  drawn  blood?  What  change 
occurs  in  it  within  a  few  minutes? 


FIG.  55.— A  white  blood- 
corpuscle,  sketched  at  suc- 
cessive intervals  of  a  few 
seconds  to  illustrate  the 
changes  of  form  due  to  its 
amoeboid  movements. 


180  THE  HUMAN  BODY. 

manent.  In  a  few  minutes  the  top  of  the  jelly-like  mass 
will  be  seen  to  be  hollowed  or  "  cupped,"  and  in  the  con- 
cavity will  be  found  a  small  quantity  of  nearly  colorless 
liquid,  the  Hood-serum.  The  jelly  next  shrinks  so  as  to 
pull  itself  loose  from  the  sides  and  bottom  of  the  vessel  con- 
taining it,  and  as  it  shrinks  it  squeezes  out  more  and  more 
serum.  Ultimately  we  get  a  solid  clot,  colored  red  and 
smaller  in  size  than  the  vessel  in  which  the  blood  coagu- 
lated, but  retaining  its  form,  and  floating  in  a  quantity  of 
pale  yellow  serum.  The  whole  series  of  changes  leading  to 
this  result  is  known  as  the  coagulation  or  clotting  of  the 
blood. 

Cause  of  Coagulation, — If  a  drop  of  fresh  drawn  blood 
be  spread  out  and  watched  with  a  powerful  microscope,  it 
will  be  seen  that  its  coagulation  is  due  to  the  separation  of 
very  fine  solid  threads  which  run  in  every  direction  through 
the  plasma  and  form  a  close  network  entangling  all  the 
corpuscles.  These  threads  are  composed  of  an  albuminous 
substance  known  as  fibrin.  When  they  first  form,  the 
whole  drop  is  much  like  a  sponge  soaked  full  of  water 
(represented  by  the  serum)  and  having  solid  bodies  (the 
corpuscles)  in  its  cavities.  After  the  fibrin  threads  have 
been  formed  they  begin  to  shorten;  hence  the  fibrinous 
network  tends  to  shrink  in  every  direction,  and  this  shrink- 
age is  greater  the  longer  the  clotted  blood  is  kept.  At  first 
the  threads  stick  too  firmly  to  the  bottom  and  sides  of  the 

What  is  meant  by  the  stage  of  gelatinization  ?  What  first  follows 
that  stage?  What  next?  What  is  the  final  result?  What  is  the  whole 
process  called? 

What  is  seen  on  watching  a  drop  of  fresh  drawn  blood  with  the 
aid  of  a  good  microscope?  What  are  the  separated  threads  composed 
of?  To  what  may  we  compare  a  drop  of  blood  in  the  first  formation 
of  the  fibrin  threads?  What  do  the  threads  do  after  their  for- 
mation? 


WHIPPED  BLOOD.  181 

vessel  to  be  pulled  away,  and  thus  the  first  sign  of  the 
contraction  of  the  fibrin  is  seen  in  the  cupping  of  the  sur- 
face of  the  gelatinized  blood  where  the  threads  have  no 
solid  attachment,  and  there  the  contracting  mass  presses 
out  from  its  meshes  "the  first  drops  of  serum.  Finally  the 
contraction  of  the  fibrin  overcomes  its  adhesion  to  the  vessel, 
and  the  clot  pulls  itself  loose  on  all  sides,  pressing  out 
more  and  more  serum.  The  great  majority  of  the  red  cor- 
puscles are  held  back  in  the  meshes  of  the  fibrin. 

Whipped  Blood. — The  essential  point  in  coagulation 
being  the  formation  of  fibrin  in  the  plasma,  and  blood  only 
forming  a  certain  amount  of  fibrin,  if  this  be  removed  as  fast 
as  it  forms  the  remaining  blood  will  not  clot.  The  fibrin 
may  be  separated  by  what  is  known  as  <e  whipping"  the 
blood.  For  this  purpose  fresh  drawn  blood  is  stirred  up 
vigorously  with  a  bunch  of  twigs  or  a  bundle  of  wire,  and 
the  sticky  fibrin  threads  as  they  form  adhere  to  these.  .  If 
the  twigs  be  then  withdrawn  a  quantity  of  stringy  material 
will  be  found  attached  to  them.  This  is  at  first  colored  red 
by  adhering  blood-corpuscles,  but  by  washing  in  water  they 
may  be  removed;  the  pure  fibrin  thus  obtained  is  perfectly 
white  and  in  the  form  of  highly  elastic  threads.  The 
"  whipped"  or  "  defibrinated  blood"  from  which  the  fibrin 
has  been  in  this  way  removed  looks  just  like  ordinary 
blood,  but  has  lost  its  power  of  coagulating  spontaneously. 

Uses  of  Coagulation. — The  living  circulating  blood  in 
the  healthy  blood-vessels  does  not  clot;  it  contains  no  solid 

Why  is  the  first  sign  of  their  contraction  seen  in  the  cupping? 
What  is  the  final  result  of  this  contraction?  Why  is  the  clot  red? 

How  can  we  prevent  blood  from  clotting?  How  is  blood 
whipped?  What  do  we  find  on  examining  the  twigs  after  whipping 
blood?  How  may  we  get  the  pure  fibrin?  What  are  its  characters? 
Give  another  name  for  whipped  blood.  How  does  it  differ  from 
ordinary  blood? 


182  THE  HUMAN  BODY. 

fibrin,  but  this  forms  in  it,  sooner  or  later,  when  the  blood 
gets  in  any  way  out  of  the  vessels  or  if  the  lining  of  these  is 
injured.  By  the  clotting  the  mouths  of  the  small  vessels 
opened  in  a  wound  are  clogged  up,  and  the  bleeding,  which 
would  otherwise  go  on  indefinitely,  is  stopped.  So  too, 
when  a  surgeon  ties  an  artery,  the  tight  ligature  crushes  or 
tears  its  delicate  inner  surface,  and  the  blood  clots  where 
this  is  injured.  The  clot  becomes  more  and  more  solid, 
and  by  the  time  the  ligature  is  removed  has  formed  a  firm 
plug  in  the  cut  end  of  the  artery,  which  prevents  bleeding. 

Blood  Compared  with  Water. — "  Leaving  aside  its  color, 
we  all  know  that  blood  is  thicker  than  water;  this  is  true 
not  only  in  a  metaphorical  but  in  a  literal  sense.  In  the 
first  place,  bulk  for  bulk,  blood  is  heavier  than  water;  ten 
teaspoonfuls  of  blood  weigh  as  much  as  ten  and  a  half  tea- 
spoonfuls  of  water.  Secondly,  blood  contains  in  it  solid 
corpuscles  and  when  drawn  from  the  body  forms  spon- 
taneously a  solid  clot,  while  pure  water  has  no  solid  bodies 
floating  in  it,  and  can  only  be  made  solid  by  freezing. 
Thirdly,  the  blood  liquid  itself,  quite  apart  from  the  cor- 
puscles, is  thicker  than  pure  water,  because  it  contains  a 
great  many  things  dissolved  in  it;  things  which  are  of  great 
importance,  because  they  are  the  foods  which  the  blood  is 
carrying  to,  and  the  wastes  which  it  is  carrying  from,  the 
various  organs  of  the  body." 

The  Composition  of  Blood-Serum.— About  one  half  of 
the  bulk  of  fresh  blood  is  corpuscles  and  the  other  half 

When  does  blood  clot?  Illustrate  the  uses  of  the  coagulating 
property  of  blood. 

Compare  blood  with  water,  (1)  as  to  the  weight  of  equal  bulks  of  the 
two  (specific  gravity);  (2)  as  to  its  microscopic  structure;  (3)  as  to  its 
tendency  to  solidify ;  (4)  as  to  the  composition  of  its  plasma.  Why 
arc  the  things  dissolved  in  the  plasma  of  great  importance? 

What  is  the  relative  proportion  of  corpuscles  and  plasma  in  blood? 


THE  COMPOSITION  OF  BLOOD-SERUM.  183 

plasma.  What  the  plasma  contains  we  may  learn  by  ex- 
amining blood-serum,  which  is  plasma  minus  fibrin. 

Blood-serum  is  very  different  from  water;  if  we  keep  on 
boiling  pure  water  in  a  saucepan  it  will  all  go  off  in  steam 
and  leave  nothing  behind,  but  if  we  try  to  boil  serum  we 
find  that  we  cannot  do  it;  before  it  gets  as  hot  as  boiling 
water  it  sets  into  a  stiff,  solid  mass  just  like  the  white  of  a 
hard-boiled  egg.  In  fact  the  serum  contains  dissolved  in  it 
an  albumen  which  is  very  like  that  in  the  white  of  an  egg, 
and  is  coagulated  in  the  same  way  by  boiling.  About  eight 
and  a  half  pounds  of  albuminous  substances  exist  in  one 
hundred  pounds  of  blood. 

Blood-serum  also  contains  considerable  quantities  of  oily 
and  fatty  matters,  a  little  sugar,  some  common  salt  and 
carbonate  of  soda,  and  small  quantities  of  very  many  other 
things,  chiefly  waste  products  from  the  various  tissues. 
Nine  tenths  of  the  blood-plasma  are  water. 

Composition  of  the  Red  Corpuscles. — In  the  fresh  moist 
state  these  contain  a  little  more  than  half  their  weight  of 
water.  Nine-tenths  of  their  solid  part  is  haemoglobin ; 
they  also  contain  phosphorus  and  iron  and  potassium. 

The  Blood  Gases. — Ordinary  fresh  or  salt  water  has  a 
good  deal  of  air  dissolved  in  it,  which  fishes  breathe.  Blood 
also  contains  a  quantity  of  gases  which  it  gives  off  when 
exposed  to  a  vacuum,  about  sixty  pints  of  gas  to  a  hundred 

What  may  we  learn  by  examining  blood-serum?  What  is  blood- 
serum? 

What  happens  when  we  try  to  boil  blood-serum?  Why  does  it 
coagulate  in  heating?  What  proportion  of  albumen  exists  in  blood? 

What  things  are  found  in  the  blood-serum  in  addition  to  water? 
JIow  much  water  is  there  in  ten  pints  of  blood-plasma? 

How  much  solids  do  the  red  corpuscles  contain?  What  propor- 
tion of  these  is  haemoglobin?  Name  other  things  found  in  the  red 
corpuscles. 

What  do  fishes  breathe?  What  does  blood  give  off  when  placed  in 
a  vacuum?  How  many  pints  of  gas  for  each  ten  of  blood? 


184  THE  HUMAN  BODY. 

pints  of  blood.  In  blood  going  to  the  lungs  the  main  gas 
is  carbon  dioxide  (or  carbonic  acid),  which  is  a  waste  product 
of  all  the  organs  of  the  body.  In  blood  coming  from  the 
lungs  the  most  abundant  gas  is  oxygen. 

Summary. — "Blood,  then,  is  a  very  wonderful  fluid: 
wonderful  for  being  made  up  of  colored  corpuscles  and 
colorless  fluid,  wonderful  for  its  fibrin  and  power  of  clot- 
ting, wonderful  for  the  many  substances,  for  the  proteids, 
for  the  ashes  or  minerals,  for  the  rest  of  the  things  which 
are  locked  up  in  the  corpuscles  and  in  the  serum. 

"  But  you  will  not  wonder  at  it  when  you  come  to  see  that 
the  blood  is  the  great  circulating  market  of  the  body,  in 
which  all  the  things,  that  are  wanted  by  all  parts,  by  the 
muscles,  by  the  brain,  by  the  skin,  by  the  lungs,  liver,  and 
kidneys,  are  bought  and  sold.  What  the  muscle  wants  it 
buys  from  the  blood;  what  it  has  done  with  it  sells  back  to 
the  blood;  and  so  with  every  other  organ  and  part.  As 
long  as  life  lasts  this  buying  and  selling  is  forever  going  on, 
and  this  is  why  the  blood  is  forever  on  the  move,  sweeping 
restlessly  from  place  to  place,  bringing  to  each  part  the 
things  it  wants,  and  carrying  away  those  with  which  it  has 
done.  When  the  blood  ceases  to  move,  the  market  is  blocked, 
the  buying  and  selling  cease,  and  all  the  organs  die,  starved 
for  the  lack  of  the  things  which  they  want,  choked  by  the 
abundance  of  things  for  which  they  have  no  longer  any 
need." — Foster. 

Hygienic  Remarks. — The  blood  flowing  from  any  organ 
will  have  lost  or  gained,  or  gained  some  things  and  lost 

What  is  the  most  abundant  gas  in  blood  going  to  the  lungs? 
What  in  that  leaving  those  organs? 

Why  may  blood  be  justly  called  a  wonderful  fluid?  Why  is  its 
complexity  not  astonishing?  Why  is  the  blood  always  kept  in  move- 
ment during  life?  What  happens  when  the  blood  ceases  to  move? 


HYGIENIC  REMARKS.  185 

others,  when  compared  with  the  blood  which  entered  it.  But 
the  losses  and  gains  in  particular  parts  of  the  body  are  in 
such  small  proportion  as,  with  the  exception  of  the  blood 
gases,  to  elude  analysis  for  the  most  part;  and,  the  blood 
from  all  parts  being  mixed  up  in  the  heart,  they  balance  one 
another  and  produce  a  tolerably  constant  average.  In 
health,  however,  the  red  corpuscles  are  present  in  greater 
proportion  to  the  plasrmi  after  a  meal  than  before  it. 
Healthy  sleep  in  proper  amount  also  increases  the  proportion 
of  red  corpuscles,  and  want  of  it  diminishes  their  number, 
as  may  be  recognized  in  the  pallid  aspect  of  a  person  who 
has  lost  several  night's  rest.  Fresh  air  and  plenty  of  it 
favors  their  increase.  The  proportion  of  these  corpuscles  has 
a  great  importance,  since  they  serve  to  carry  oxygen,  which 
is  necessary  for  the  performance  of  its  functions,  all  over 
the  body.  Ancemia  is  a  diseased  condition  characterised 
by  pallor  due  to  deficiency  of  red  blood-corpuscles,  and  ac-1 
companied  by  languor  and  listlessness.  It  is  not  unfrequent 
in  young  girls  on  the  verge  of  womanhood,  and  in  persons 
overworked  and  confined  within  doors.  In  such  cases  the 
best  remedies  are  open-air  exercise  and  good  food,  though  \ 
medicines  containing  iron  are  often  of  great  use. 

The  Quantity  of  Blood  in  the  Body.— The  total"  weight 
of  the  blood  is  about  one-thirteenth  of  that  of  the  whole 


What  would  we  find  on  comparing  the  blood  leaving  an  organ 
•with  that  which  entered  it?  What  losses  and  gains  are  most  easily 
detected?  How  is  it  that  the  blood  maintains  a  tolerably  uniform 
average  composition  ?  How  does  a  meal  affect  the  proportion  of  red 
corpuscles?  How  does  sleep  ?  Illustrate.  What  is  the  influence  of 
plenty  of  fresh  air  ?  Why  is  the  proportion  of  blood-corpuscles  im- 
portant ?  What  is  anaemia  ?  What  class  of  persons  is  apt  to  suffer 
from  it  ?  What  are  the  best  remedies  for  it  ? 

What  is  the  proportion  of  the  weight  of  blood  to  that  of  the 
whole  body? 


186  THE  HUMAN  BODY. 

body;  a  man  of  average  size  contains  about  twelve  pounds 
of  bloodc 

The  Lymph. — The  blood  lies  every  where  in  closed  tubes, 
and  consequently  does  not  come  into  direct  contact  with 
any  of  the  cells  which  make  up  the  body,  except  those  which 
float  in  it  and  those  which  line  the  interior  of  the  blood- 
vessels. At  two  parts  of  its  course,  however,  the  vessels 
through  which  it  passes  have  extremely  thin  walls,  and 
through  the  walls  of  these  capillaries  liquid  transudes 
and  bathes  the  various  tissues.  The  transuded 
liquid  is  called  lymph;  thejblood  makes  lymph, 
and  the  lymph  directly  nourishes  all  the  tis- 
sues except  those  mentioned  above,  with  which 
the  blood  itself  comes  in  contact. 

Dialysis. — When  two  specimens  of  water 

FIG.OO. — A  dia- 

containing  different  matters  in  solution  are 
separated  from  one  another  by  a  moist  animal 
membrane,  an  interchange  of  material  will  %  m5staanimai 
take  place  under  certain  conditions.  If  A  be  membrane- 
a  vessel  (Fig.  56),  completely  divided  vertically  by  such  a 
membrane,  and  a  solution  of  common  salt  in  water  be 
placed  on  the  side  b,  and  a  solution  of  sugar  in  water  on 
the  side  <?,  it  will  be  found  after  a  time  that  some  salt  has 
got  into  c  and  some  sugar  into  b,  although  there  are  no 
visible  pores  in  the  partition.  Such  an  interchange  is  said 
to  be  due  to  dialysis  or  osmosis,  and  if  the  process  were 

How  much  blood  is  there  in  an  average  sized  man? 

Why  does  the  blood  not  directly  bathe  most  of  the  tissues?  What 
cells  come  in  contact  with  it?  What  are  the  capillaries?  What  is 
lymph?  What  is  the  nutritive  function  of  lymph? 

What  happens  when  watery  solutions  of  different  substances 
are  separated  by  a  moist  animal  membrane?  Illustrate.  What  is 
such  an  interchange  called?  What  would  be  the  result  at  the  end  of 
some  hours? 


THE  RENEWAL  OF  THE  LYMPH.  187 

allowed  to  go  on  for  some  hours  the  same  proportions  of 
salt  and  sugar  would  be  found  in  the  solutions  on  each  side 
of  the  dividing  membrane. 

The  Renewal  of  the  Lymph.— Osmotic  processes  play  a 
great  part  in  the  nutritive  processes  of  the  body.  The 
lymph  present  in  any  organ  gives  up  things  to  the  cells 
there  and  gets  things  from  them;  and  so,  although  it  may 
have  originally  been  tolerably  like  the  liquid  part  or  plasma 
of  the  blood,  it  soon  acquires  a  different  chemical  composi- 
tion. Dialysis  then  commences  between  the  lymph  out- 
side and  the  blood  inside  the  capillaries,  and  the  latter 
gives  up  to  the  lymph  new  materials  in  place  of  those  which  j 
it  has  lost,  and  takes  from  it  the  waste  products  which  it  / 
has  received  from  the  tissues.  When  this  blood,  thus  al-  / 
tered  by  exchanges  with  the  lymph,  gets  again  to  the  stom- 
ach and  intestines,  having  lost  some  food  materials,  it  is 
poorer  in  these  than  the  richly  supplied  lymph  around  their 
cells,  and  takes  up  a  supply  by  dialysis  from  it.  When  it 
reaches  the  excretory  organs  it  has  previously  picked  up  a 
quantity  of  waste  matters,  and  loses  these  by  dialysis  to  the  ' 
lymph  there  present,  which  is  specially  poor  in  such  mat- 
ters, since  the  excretory  organs  constantly  deprive  it  of 
them.  In  consequence  of  the  different  wants  and  wastes 
of  various  cells,  and  of  the  same  cells  at  different  times, 
the  lymph  must  vary  considerably  in  composition  in  various 
organs  of  the  body,  and  the  blood  flowing  through  them 
will  in  consequence  get  and  lose  different  things  in  differ- 
How  does  the  lymph  in  an  organ  come  to  differ  chemically  from 
the  blood  plasma  which  supplied  it?  What  results?  What  happens 
when  the  blood  thus  changed  reaches  stomach  or  intestine  ?  What 
when  it  reaches  excretory  organs  ?  Why  does  the  lymph  vary  in 
composition  in  different  parts  of  the  body  ?  How  does  this  affect 
the  blood  ? 


188  THE  HUMAN  BODY 

ent  places.  But,  receiving  in  its  passage  through  one  re- 
gion what  it  loses  in  another,  its  average  composition  is 
kept  pretty  constant; and,  through  interchange  with  it,  the 
average  composition  of  the  lymph  also. 

The  Lymphatic  Vessels  or  Absorbents. — The  blood,  on 
the  whole,  loses  more  liquid  to  the  lymph  through  the  cap- 
illary walls  than  it  receives  back  at  the  same  time.  This  de- 
pends mainly  on  the  fact  that  the  pressure  on  the  blood  in- 
side the  vessels  is  greater  than  that  on  the  lymph  outside, 
and  so  a  certain  amount  of  filtration  of  liquid  from  within 
out  occurs  through  the  vascular  wall,  in  addition  to  the 
dialysis.  The  excess  is*  collected  from  the  various  organs 
of  the  body  into  a  set  of  lymphatic  vessels,  which  carry  it 
directly  back  into  some  of  the  larger  blood-vessels  near 
where  these  empty  into  the  heart;  and  as  fast  as  this  on- 
ward flow  of  the  lymph  occurs  under  pressure  from  behind, 
it  is  renewed  in  the  different  organs,  fresh  liquid  filtering 
through  the  capillaries  to  take  its  place  as  fast  as  the  old  is 
drained  off. 

Since  the  lymphatic  vessels  may  be  said  to  take  up  or 
absorb  the  excess  of  liquid  drained  from  the  blood  and  also 
the  effete  matters  of  the  various  organs,  they  are  frequently 
called  the  absorbents. 

Lacteals  we  have  already  learned  to  be  only  another 
name  for  the  absorbents  of  the  small  intestine  (p.  147). 

How  is  the  average  composition  of  the  blood  maintained?  How 
that  of  the  lymph? 

Give  another  name  for  the  lymphatic  vessels.  Does  the  blood  on 
the  whole  gain  or  lose  liquid  to  the  lymph  as  it  flows  through  the  cap- 
illaries ?  Explain  why.  What  becomes  of  the  excess  of  liquid 
drained  off  from  the  blood  ? 

Where  do  the  lymphatic  vessels  convey  it?  What  produces  the 
onward  flow  of  lymph?  How  is  the  lymph  thus  drained  off  replaced? 
Why  are  the  lymphatics  called  absorbents? 

What  is  meant  by  the  lacteals? 


HISTOLOGY  AND  CHEMISTRY  OF  LYMPH.       189 

Histology  of  Lymph. — Pure  lymph  is  a  colorless,  watery 
looking  liquid;  examined  with  a  microscope  it  is  seen  to 
contain  numerous  pale  corpuscles  exactly  like  those  of  the 
blood.  It  contains  none  of  the  red  corpuscles. 

Chemistry  of  Lymph. — Lymph  is  not  quite  so  heavy  as 
blood,  though  heavier  than  water.  It  may  be  described  as 
blood  minus  its  red  corpuscles  and  considerably  diluted, 
but  of  course  in  various  parts  of  the  body  it  will  contain 
minute  quantities  of  substances  derived  from  neighboring 
tissues. 

Summary. — To  sum  up:  the  blood  and  lymph  pro- 
vide a  liquid  in  which  the  tissues  of  the  body  live;  the 
lymph  is  derived  from  the  blood,  and  affords  the  immedi- 
ate nourishment  of  the  great  majority  of  the  living  cells  of 
the  body;  the  excess  of  it  is  finally  returned  to  the  blood, 
which  indirectly  nourishes  the  cells  by  keeping  up  the 
stock  of  lymph.  The  lymph  itself  moves  but  slowly,  but 
it  is  constantly  renovated  by  interchanges  with  the  blood, 
which  is  kept  in  rapid  movement  by  the  heart,  and  which, 
besides  containing  a  store  of  new  food-matters  for  the  lymph, 
absorbs  the  wastes  which  the  various  cells  have  poured  into 
the  latter. 

What  does  lymph  look  like?  What  is  seen  when  it  is  examined 
with  a  microscope? 

How  does  lymph  differ  in  density  from  blood  and  from  water? 
How  may  it  be  briefly  described?  What  does  it  contain  in  various 
regions  of  the  bod}^? 

What  do  the  blood  and  lymph  provide?  Whence  is  the  lymph  de- 
rived? What  does  it  afford?  What  becomes  of  its  excess?  How 
does  the  blood  play  a  part  in  nourishing  the  cells  of  the  body? 
Which  moves  faster,  lymph  or  blood?  How  is  the  lymph  renovated? 
What  keeps  the  blood  in  motion?  What  does  the  blood  do  besides 
renewing  the  food-matters  in  the  lymph? 


190  THE  HUMAN  BODY, 


APPENDIX  TO  CHAPTER  XIII. 

Many  of  the  main  facts  pertaining  to  the  structure  and  composi- 
tion of  blood  may  be  easily  demonstrated  as  follows: 

1.  Kill  a  frog  with  ether  (note,  p.  68);  cut  off  its  head,  and  collect 
on  a  piece  of  glass  a  drop  of  the  blood  which  flows  out.     Spread  out 
the  drop  so  that  it  forms  a  thin  layer.     Hold  the  glass  up  against  the 
light,  and  examine  the  blood  with  a  hand  lens  magnifying  four  or  five 
diameters.  The  corpuscles  will  be  readily  seen  floating  in  the  plasma. 

2.  Wind  tightly  a  piece  of  twine  around  the  last  joint  of  a  finger; 
then,  taking  a  needle,  prick  the  skin  near  the  root  of  the  nail.     A 
large  drop  of  blood  will  exude.     Spread  it  out  on  a  piece  of  glass 
and  examine,  as  described  above  for  frog's  blood.     The  corpuscles 
will  be  seen  floating  in  the  blood  liquid,  but  not  so  easily  as  in  frog's 
blood,  sinc^e  those  of  man  are  considerably  smaller. 

[3.  If*a  compound  microscope  is  available  the  form,  size,  and 
color  of  human  and  frog  red  blood-corpuscles  can  be  demonstrated; 
also  the  tendency  of  the  human  to  aggregate  in  rolls,  and  the  color, 
form,  size,  and  relative  number  of  tha  colorless  corpuscles.  As  any 
one  possessing  a  compound  microscope  is  sure  to  know  how  to 
mount  a  specimen  of  blood  for  examination  with  it,  or,  if  not,  to 
have  at  hand  some  treatise  on  the  use  of  the  microscope  giving  the 
necessary  information,  details  need  not  be  given  here.] 

4.  Obtaining  a  large  drop  of  human  blood  as  above  described  (2) 
— note:  a,  that  as  it  flows  from  the  wound  it  is  perfectly  liquid;  b, 
that  it  is  red  and  very  opaque;  c,  spread  it  out  very  thin  on  the  glass; 
note  that  it  then  looks  yellow  when  held  over  a  sheet  of  white  paper; 
d,  mix  a  similar  drop  with  a  teaspoonful  of  water  in  a  wine  glass; 
note  that  the  mixture  is  yellowish,  or,  if  not,  becomes  so  on  further 
dilution. 

5.  Place  another  large  drop  of  human  blood,  obtained  as  above 
indicated,  on  a  clean  glass  plate.     To  prevent  drying  up  cover  by 
in  verting  over  the  drop  a  wine  glass  whose  interior  has  been  moistened 
with  water.     In  four  or  five  minutes  remove  the  wine-glass  and  note 
that  the  blood  drop  has  set  into  a  firm  jelly.     Replace  the  moist 
wine-glass;  and  in  half  an  hour  examine  again.     The  blood  will  then 
have  separated  into  a  tiny  red  clot,  lying  in  nearly  colorless  serum. 

6.  If  a  slaughter-house  is  accessible  the  clotting  of  blood  may  be 
still  better  illustrated.     Provide  two  large  wide-necked  glass  bottles 
and  a  bundle  of  twigs.     When  the  butcher  bleeds  an  animal  collect 
in  one  bottle  some  blood,  taking  care  that  nothing  else  (contents  of 


APPENDIX.  191 

the  stomach,  for  example,  when  the  animal  is  bled,  as  is  often  done, 
by  cutting  off  its  head)  gets  mixed  with  it.  Put  this  bottle  aside 
until  the  blood  clots,  and  carry  it  home  with  the  least  possible 
shaking.  Next  day  the  mass  will  exhibit  a  beautiful  clot  floating  in 
serum.  The  latter  will  probably  be  tinted  red,  as  the  jolting  in 
conveying  the  specimen  from  the  slaughter-house  shakes  some  of  the 
corpuscles  out  of  the  clot  into  the  serum. 

7.  In  the  other  bottle  collect  blood  and  beat  it  vigorously  with  the 
twigs  for  three  or  four  minutes.     Next  day  this  specimen  will  not 
have  clotted,  but  on  the  twigs  will  be  found  a  quantity  of  stringy 
elastic  material  (fibrin),  which  becomes  pure  white  when  thoroughly 
washed  with  water. 

8.  Take  some  of  the  serum  from  specimen  6.     Point  out  that  it 
does  not  coagulate  spontaneously.     Heat  it  in  a  test  tube  over  a  spirit 
lamp;  the  albumen  will  be  coagulated  and  the  whole  will  become 
solid. 

9.  Place  a  small  quantity  of  whipped  blood  (7)  on  a  piece  of 
platinum  foil.     Heat  over  a  spirit  lamp.     After  the  drop  dries  it 
blackens,  showing  that  it  contains  much  organic  matter.     As  the 
heating  is  continued  this  is  burnt  away,  and  a  white  ash,  consisting 
of  the  mineral  constituents  of  the  blood,  is  left. 


CHAPTER  XIV. 
THE  ANATOMY  OF  THE  CIRCULATORY  ORGANS. 

The  Organs  of  Circulation  are  the  heart  and  the  blood- 
vessels; the  blood-vessels  are  of  three  kinds,  arteries,  capil- 
laries, and  veins.  The  arteries  carry  blood  from  the  heart 
to  the  capillaries;  the  veins  collect  it  from  the  capillaries 
and  return  it  to  the  heart.  There  are  two  distinct  sets  of 
blood-vessels  in  the  body,  both  connected  witlT^he  heart; 
one  set  carries  blood  to,  through,  and  from  the  lungs,  the 
other  guides  its  flow  through  all  the  remaining  organs;  the 
former  are  known  as  the  pulmonary,  the  latter  as  the  sys- 
temic blood-vessels. 

General  Statement. — During  life  the  pumping  of  the 
heart  keeps  the  blood  flowing  rapidly  through  the  paths 
marked  out  for  it  by  the  blood-vessels  ;  these  paths  it  never 
leaves  except  in  cases  of  disease  or  injury. 

The  blood-vessels  form  a  continuous  system  of  closed 
tubes  comparable  in  a  certain  way  to  the  water-mains  of  a 
city.  These  tubes  begin  at  the  heart,  and  are  very  much 
branched  except  close  to  it,  just  as  the  water  pipes  are 
single  only  where  the  main  aqueduct  leaves  the  reservoir, 

Name  the  organs  of  circulation.  Name  the  kinds  of  blood-ves- 
sels. What  is  the  function  of  the  arteries?  Of  the  veins?  How 
many  sets  of  blood-vessels  are  there  in  the  body?  What  does  each 
set  do?  What  are  they  called? 

What  is  brought  about  by  the  beat  of  the  heart?  Under  what 
circumstances  may  blood  leave  a  blood  channel? 

What  do  the  blood-vessels  form?  Illustrate  their  function  by 
comparison  with  the  water-mains  of  a  city. 

r!921 


PLATE   IV.— THE   CHIEF   ARTKRIES   AND   VEINS   OF   THK   BODY. 


EXPLANATION  OF  PLATE  IV. 
THE  CIRCULATORY  ORGANS. 

The  arteries  (except  the  pulmonary)  and  the  left  side  of  the  heart 
are  colored  red;  the  veins,  (except  the  pulmonary)  and  the  right  half 
of  the  heart  blue:  on  the  limbs  of  the  left  side  the  arteries  are  omitted 
and  only  the  superficial  veins  are  shown. 

1.  Aorta,  near  its  origin  from  the  left  ventricle  of  the  heart. 

2.  Lower  end  of  aorta. 

3.  Iliac  artery. 

4.  Femoral  artery. 

5.  Popliteal  artery;  the  continuation  of  the  femoral  which  passes  behind  the 

knee-joint. 

6.  7.  The  main  trunks  (anterior  and  posterior  tibial  arteries  into  which  the 

popliteal  divides). 

8.  Subclavian  artery. 

9.  Brachial  artery. 

10.  Radial  artery. 

11.  Ulnar  artery. 

12.  Common  carotid  artery. 

13.  Facial  artery. 

14.  Temporal  artery. 

15.»Right  side  of  Heart,  with  superior  vena  cava  joining  it  above,  and  inferior 
vena  cava  (16)  passing  up  to  it  from  below. 

17.  Innominate  vein,  formed  by  the  union  of  subclavian  and  jugular  veins. 

The  right  and  left  innominate  veins  unite  to  form  the  superior  cava. 

18.  Left  internal  jugular  vein. 

19.  Axillary  vein. 

20.  Basilic  vein. 

22.  Cephalic  vein. 

23.  Radial  vein. 

24.  Ulnar  vein. 

25.  Median  vein. 

26.  Iliac  vein. 

27.  Femoral  vein 

28.  Long  saphenous  vein. 

29.  The  kidney;  attached  to  it  are  seen  the  renal  artery  and  vein. 

30.  Branches  of  the  pulmonary  arteries  and  veins  in  the  lung. 


FUNCTIONS  OF  THE   VASCULAR  SYSTEM.       193 

and  more  and  more  divided  the  further  one  follows  them 
from  that  point,  until,  in  the  various  houses,  they  end  in 
numerous  but  very  much  smaller  tubes.  The  course  of  the 
blood  differs,  however,  essentially  from  that  of  the  water 
supplied  to  a  city,  for  the  water  does  not  return  to  the 
reservoir,  whereas  the  blood  is  carried  back  to  the  heart: 
instead  Of  having  a  large  supply  of  liquid  stored  up  as  in 
a  reservoir,  there  is  at  any  one  time  only  quite  a  small 
amount  in  the  heart,  but  this  is  steadily  replaced  by  the  in- 
flow through  the  veins  as  fast  as  it  is  carried  o2  by  outflow 
through  the  arteries. 

General  Functions  of  the  Different  Parts  of  the  Vascular 
System. — The  blood  vascular  system  is  quite  closed  except  at 
two  points,  one  on  each  side  of  the  neck,  where  lymph  vessels 
pour  the  excess  of  lymph  back  into  the  veins.  Valves  at 
these  two  points  let  lymph  flow  into  the  blood-vessels,  but 
will  not  allow  blood  to  pass  the  other  way.  Accordingly 
everything  which  leaves  the  blood  must  do  so  by  oozing 
through  the  walls  of  the  blood-vessels,  and  everything 
which  enters  it  must  do  the  same,  except  matters  conveyed 
in  by  the  lymph  at  the  points  above  mentioned:  This  inter- 
change through  the  walls  of  the  vessels  takes  place  only  in 
the  capillaries.  In  India  where  rain  only  falls  at  certain 
seasons  it  is  stored  up  in  huge  tanks,  and  during  the  subse- 
quent dry  months  distributed  over  the  fields  by  a  set  of 
small  ditches  and  channels,  cut  through  them  in  all  direc- 
tions, and  from  which  the  liquid  soaks  through  the  sur- 

How  does  the  blood  flow  differ  from  that  of  water  in  the  mains 
of  a  city?  How  is  the  supply  of  blood  in  the  heart  kept  up? 

Where  is  the  blood  vascular  system  not  closed?  Wliat  occurs  at  its 
openings?  What  is  the  function  of  the  valves  at  these  openings?  How 
must  substances  leave  the  blood  ?  How  enter  it?  In  what  vessels  does 
interchange  through  the  walls  of  the  blood-vessels  occur?  Illustrate  the 
function  of  the  capillaries  by  comparison  with  an  irrigation  system. 


194 


THE  HUMAN  BODY. 


rounding  soil;  this  is  known  as  irrigation,  and  the  capillaries 
may  be  said  to  form  an  irrigation  system  for  the  body.  In 
a  certain  sense  also  they  may  be  compared  to  the  water 
spigots  of  a  house,  which  lie  at  the  end  of  the  supply  tubes, 
the  arteries;  but,  to  make  the  comparison  more  accurate, 
we  would  have  to  imagine  instead  of  ordinary  spigots  bags 
of  very  fine  muslin  through  which  ,the  water  oozed  when 
the  tap  was  turned  on.  The  capillaries,  though  far  the 
smallest  tubes  in  the  vascular  system,  are 
the  really  important  parts;  the  heart, 
arteries,  and  veins  are  all  merely  ar- 
rangements for  keeping  the  capillaries 
full,  and  renewing  the  blood  within 
them.  It  is  while  flowing  through  these 
and  soaking  through  their  walls  that  the 
blood  does  its  physiological  work. 

Diagram  of  the  Circulatory  Organs. — •. 
The  general  relationship  of  heart,  arte- 
ries, capillaries,  and  veins  may  be  gath- 
ered from  the  accompanying  diagram 
(Fig.  57).  The  heart  is  essentially  a  bag 
with  muscular  walls,  and  internally  di- 
FIG.  57.— The  heart  vided  into  four  chambers  (d,  g,  e,  /). 

and   blood-vessels  dia-  ,  7         .     N  -ITT 

grammatically    repre-     TllOSC  at  0116  end  (d  and  6)  1'GCeiVe  blood 

from  vessels  opening  into  them  and 
known  as  the  veins.  From  there  the  blood  passes  on  to 
the  remaining  chambers  (g  and/),  which  have  very  mus- 
cular walls  and,  forcibly  contracting, drive  the  blood  out  into 


By  comparison  with  the  water  pipes  of  a  house.  What  is  the 
use  of  heart,  arteries,  and  veins?  When  does  the  blood  do  its  physi- 
ological work? 

Sketch  on  the  blackboard  a  diagram  of  the  circulatory  organs. 
What  is  briefly  the  structure  of  the  heart?  Where  does  the  blood 
enter  the  heart?  From  what  vessels?  Where  does  it  go  next? 


THE  POSITION  OF  THE  HEART.  195 

vessels  (i  and  b)  which,  communicate  with  them  and 
are  known  as  the  arteries.  The  big  arteries  divide  into 
smaller;  these  into  smaller  again  (Plate  IV),  until  the 
branches  become  too  small  to  be  traced  by  the  unaided  eye, 
and  these  smallest  branches  end  in  the  capillaries,  through 
which  the  blood  flows  and  enters  the  commencements  of  the 
veins ;  the  veins  convey  it  again  to  the  heart.  At  certain 
points  in  the  course  of  the  blood-path  valves  are  placed, 
which  prevent  a  back-flow.  This  alternating  reception  of 
blood  at  one  end  of  the  heart  and  its  ejection  from  the 
other  occurs  about  seventy  times  a  minute  during  health. 

The  Position  of  the  Heart. — The  heart  (Ji,  Fig.  4)  lies 
in  the  chest,  immediately  above  the  diaphragm  and  opposite 
the  lower  two  thirds  of  the  breast-bone.  It  is  conical  in 
form,  with  its  base  or  broader  end  turned  upwards  and  pro- 
jecting a  little  on  the  right  of  the  sternum,  while  its  nar- 
row end  or  apex,  turned  downwards,  projects  to  the  left  of 
that  bone,  where  it  may  be  felt  beating  between  the  carti- 
lages of  the  fifth  and  sixth  ribs.  The  position  of  the  organ 
in  the  body  is,  therefore,  oblique.  It  does  not,  however,  lie 
on  the  left  side,  as  is  so  commonly  believed,  but  very  nearly 
in  the  middle  line,  with  the  upper  part  inclined  to  the 
right,  and  the  lower  (which  may  be  more  easily  felt  beat- 
ing— hence  the  common  belief)  to  the  left. 

The  Pericardium. — The  heart  does  not  lie  bare  in  the 


What  then  happens  to  it?  How  are  the  small  arteries  formed? 
In  what  vessels  do  they  end?  What  becomes  of  blood  which  has 
flowed  through  the  capillaries?  Where  do  the  veins  carry  it?  How 
is  back-flow  prevented?  How  frequently  does  the  heart  receive  and 
pump  out  blood? 

Where  is  the  heart  situated?  What  is  its  form?  Where  does  its 
base  lie?  Where  its  apex?  Where  may  we  feel  the  apex  beat? 
What  is  the  origin  of  the  common  belief  that  the  heart  is  on  the  left 
side? 


[96  THE  HUMAN  BODY. 

chest,  but  is  surrounded  by  a  loose  bag  composed  of  con- 
nective tissue  and  called  the  pericardium.  This  bag,  like 
the  heart,  is  conical  but  turned  the  other  way,  its  broad 
part  being  lowest  and  attached  to  the  upper  surface  of  the 
diaphragm.  Internally  it  is  lined  by  a  smooth  serous  mem- 
brane like  that  lining  the  abdominal  cavity,  and  a  similar 
layer  (the  visceral  layer  of  the  pericardium)  covers  the  out- 
side of  the  heart  itself,  adhering  closely  to  it.  In  the  space 
between  the  serous  membranes  is  a  small  quantity  of  liquid 
which  moistens  the  contiguous  surfaces,  and  diminishes  the 
friction  which  would  otherwise  occur  during  the  movements 
of  the  heart. 

Suppose  a  pear  put  in  a  bag  of  about  the  same  shape, 
but  larger,  and  turned  the  other  way  so  that  the  big  end 
of  the  bag  was  round  the  small  end  of  the  pear;  then  you 
will  get  a  good  idea  of  how  the  pericardium  lies  with  refer- 
ence to  the  heart.  If  the  outside  of  the  pear  and  the  inside 
of  the  bag  were  covered  with  paint,  this  would  represent 
the  serous  membrane,  and  a  few  drops  of  water  between  the 
pear  and  the  bag  would  represent  the  serous  liquid.  To 
complete  the  comparison  we  may  imagine  the  pear  to 
have  eight  or  nine  stalks  which  reached  out  from  it  through 
the  bag;  these  would  answer  to  the  blood-vessels  entering 
and  leaving  the  heart. 

Note. — Sometimes  the  pericardium  becomes  inflamed, 
this  affection  being  known  as  pericarditis.  It  is  extremely 
apt  to  occur  in  rheumatic  fever,  and  extreme  care  should 
be  taken  never,  even  for  a  moment,  except  under  medical 

What  is  the  pericardium?  What  is  its  form?  What  lines  it? 
What  covers  the  outside  of  the  heart?  What  lies  between  the  visceral 
layer  of  the  pericardium  and  the  outer  bag?  What  is  its  use? 

Illustrate  the  relations  of  heart  and  pericardium. 

What  is  pericarditis?     In  what  disease  is  it  especially  apt  to  occur? 


CAVITIES  OF  THE  HEART.  197 

advice,  to  expose  a  patient  to  cold  during  that  disease, 
since  any  chill  is  then  especially  apt  to  set  up  pericarditis. 
In  the  earlier  stages  of  pericardiac  inflammation  the  rub- 
bing surfaces  on  the  outside  of  the  heart  and  the  inside  of 
the  pericardium  become  roughened,  and  their  friction  pro- 
duces a  sound  which  can  be  heard  with  a  stethoscope.  In 
later  stages  great  quantities  of  liquid  may  accumulate  in 
the  pericardium  so  as  to  seriously  impede  the  heart's  beat. 

The  Cavities  of  the  Heart. — On  opening  the  heart  (see 
diagram,  Fig.  57,  p.  194)  it  is  found  to  be  subdivided  by  a 
'longitudinal  partition  or  septum  into  completely  separated 
right  and  left  halves,  the  partition  running  from  about  the 
'middle  of  the  base  to  a  point  a  little  on  the  right  of  the  apex. 
Each  of  the  chambers  on  the  sides  of  the  septum  is  again 
incompletely  divided  transversely  into  a  thinner  basal  por- 
tion into  which  veins  open,  known  as  the  auricle,  and  a 
thicker  apical  portion  from  which  arteries  arise  and  called 
the  ventricle.  The  heart  cavity  thus  consists  of  a  right 
auricle  and  ventricle  and  a  left  auricle  and  ventricle,  each 
auricle  communicating  by  an  auriculo-ventricular  orifice 
with  the  ventricle  on  its  own  side;  there  is  no  direct  com- 
munication whatever  through  the  septum  between  the  op- 
posite sides  of  the  heart.  To  get  from  one  side  to  the  other 
the  blood  must  leave  the  heart  and  pass  through  a  set  of 


Why  should  a  person  with  rheumatic  fever  never  be  'exposed 
to  cold  except  under  skilled  advice?  What  can  be  heard  with  a 
stethoscope  in  the  early  stages  of  pericarditis?  What  may  occur  in 
its  later  stages? 

What  is  seen  on  opening  the  heart?  In  what  direction  does  the 
septum  run?  What  is  an  auricle?  A  ventricle?  Enumerate  the 
Chambers  of  the  heart  cavity.  With  what  does  each  auricle  com- 
municate? Is  there  a  direct  connection  between  the  right  and  left 
sides  of  the  heart?  What  must  the  blood  do  to  get  from  one  side  of 
the  heart  to  the  other? 


198 


THE    HUMAN   BODY. 


capillaries,  as  may  readily  be  seen  by  tracing  the  course  of 

the  vessels  in  Fig.  57. 

The  Vessels  connected  with  the  Different  Chambers  of 

the  Heart. — One  big  ar- 
tery, called  the  aorta, 
springs  from  the  left 
ventricle ;  it  runs  back 
to  the  pelvis  after  giving 
off  very  many  branches" 
on  its  way  and  then  di- 
vides into  an  artery  for 
each  leg.  Its  big  branches 
divide  into  smaller  and 
these  into  smaller  again,- 
until  they  become  too 
small  to  be  traced  by  the 
unaided  eye.  They  spread 
through  the  whole  body, 
to  muscles,  and  bones, 
and  skin,  and  brain,  and 
stomach,  and  intestines, 

PIG.  58.— VIEW  op  THE   HEART   AND  GREAT    QTirl    liVnv     nnrl    Virlnpvc  • 
VESSELS  FROM  BEFORE.  ana   liver,   ana    Kianeys  , 

The  pulmonary  artery  has  been  cat  short  thev  finally  end  HI  the  SVS- 

close  to  its  origin.      1,  right  ventricle  ;'  2,  left  "               \ 

ventricle;  3,  root  of  the  pulmonary  artery;  4,  temiC     Capillaries          The 
4',  arch  of  the  aorta;  4",  the  descending  thoracic, 

aorta;  5,  part  of  the  right  auricle;  6,  part  of  the  svstemio  VPl*n<? 

left  auricle;  7,7',  innominate  veins  joining  to  *B 
form  the  vena  cava  superior;    8,  inferior  vena_  TYInnd    fvrkTVl      f 

cava;  9,  one  of  the   large   hepatic  veins  ;  X,  Di°°a    irom     t 

placed  in  the  right  aurictilo- ventricular  groove,  •            «    ,,         -,.„. 

points  to  the  right  or  posterior  coronary  artery  ;  *     8   OI    tne    Uluerent 

X,  X,  placed  in  the  anterior  interventricular  j      n    ii 

groove,  indicate  the  left  or  anterior  coronary  ganS,  and  all  tnese 
artery. 

What  artery  arises  from  the  left  ventricle  t  To  what  point  does 
it  run?  What  does  it  give  off  on  its  course?  How  does  it  end?  What 
becomes  of  its  branches?  In  what  do  they  end?  What  vessels  col- 
lect the  blood  from  the  systemic  capillaries? 


VESSELS  CONNECTED    WITH  THE  HEAEJ\      199 

unite  to  form  the  superior  and  inferior  vencB  caves  or 
the  upper  and  lower  hollow  veins.  These  carry  the  blood 
to  tlie  jiglit-awriele ;  thence  it  enters  the  right  ventricle 
from  which  arises  one  vessel,  the  pulmonary  artery ;  tins 
divides  into  a  branch  for  each  lung  ;  each  branch  splits  up 
into  minute  arteries  in  its  own  lung,  and  these  end  in  the 
pulmonary  capillaries.  From  the  pulmonary  capillaries  the 
blood  of  each  lung  is  collected  into  two  pulmonary  veins, 
and  the  four  pulmonary  veins  open  into  the  left  auricle. 

Summary. — One  artery,  the  aorta,  arises  from  the  left 
ventricle.  The  blood  carried  out  by  the  aorta  comes  back 
by  the  upper  and  lower  venae  cavae  to  the  right  auricle;  this 
blood  then  goes  to  the  right  ventricle  and  is  sent  thence 
through  the  pulmonary  artery,  which  splits  up  into  branches 
for  the  lungs.  The  blood,  carried  out  by  the  pulmonary 
artery  from  the  right  ventricle  of  the  heart,  returns  to  the 
left  auricle  by  four  pulmonary  veins,  two  from  each  lung; 
and  then  enters  the  left  ventricle  and  begins  its  flow  again 
through 'the  aorta. 

How  the  Heart  is  Nourished. — The  heart  is  a  very  hard- 
worked  organ,  and  needs  an  abundant  supply  of  nourish- 
ment. Its  walls  are  much  too  thick  to  allow  this  to  soak 
in  sufficient  abundance  all  through  them,  from  the  blood 
flowing  through  its  cavities  ;  accordingly  they  are  perme- 
ated by  a  very  close  network  of  capillary  blood  v  vessel .. 
These  are  supplied  by  the  right  and  left  coronary  arteries 

Where  do  the  venae  cavse  carry  it?  Where  d«es  it  pass  from  the 
right  auricle?  What  vessel  arises  from  the  right  ventricle?  Into 
what  does  the  pulmonary  artery  divide?  What  happens  to  each 
branch?  How  do  the  branches  finally  end?  Into  what  is  the  blood 
which  flows  through  the  pulmonary  capillaries  collected?  How 
many  pulmonary  veins  are  there?  Where  do  they  end? 

State  briefly  the  course  of  the  blood  flow. 


200 


THE    HUMAN   BODY. 


(Fig.  58),  which  are  the  two  very  first  branches  of  the 
aorta,  and  the  blood  from  them  is  collected  by  the  coronary 
veins  and  poured  by  them  directly  into  the  right  auricle. 

Sp 


S-l 


Mpl 


Mpm 


FIG.  59. — The  left  ventricle  and  the  commencement  of  the  aorta  laid  open. 
flfpl.  the  papillary  muscles.  From  their  upper  ends  are  seen  the  chordae  tendineae 
proceeding  to  the  edges  of  the  flaps  of  the  mitral  valve.  The  opening  into  the 
auricle  lies  between  these  flaps.  At  the  beginning  of  the  aorta  arc  seen  its  three 
pouch-like  semilunar  valves. 


What  are  the  coronary  arteries  ?    The  coronary  veins  ? 


AUR1CULO-VENTRICULAR    VALVES.  201 

The  Auriculo-Ventricular  Valves. — Between  eacL  auricle 
of  the  heart  and  the  ventricle  of  the  same  side  are  found 
valves  which  allow  blood  to  pass  from  the  auricle  to  the 
ventricle,  but  prevent  any  flow  in  the  opposite  direction. 
These  valves  are  known  as  the  tricuspid  and  mitral  valves. 
The  mitral  valve  (Fig.  59)  consists  of  two  flaps  fixed  by 
their  bases  to  the  margins  of  the  opening  between  the  left 
auricle  and  the  left  ventricle ;  their  edges  hang  down  into 
the  ventricle  when  the  heart  is  empty.  These  edges  are  not 
free,  but  have  fixed  to  them  a  number  of  stout  connective- 
tissue  cords,  the  chorda  tendinece,  which  are  fixed  below  to 
muscular  elevations,  the  papillary  muscles,  Mpm  and  Mpl, 
on  the  interior  of  the  ventricle.  The  cords  are  long  enough 
to  let  the  valve  flaps  rise  into  a  horizontal  position  and  so 
to  close  the  opening  between  auricle  and  ventricle, which 
lies  behind  the  opened  aorta,  Sp,  represented  in  the  figure. 
The  tricuspid  valve  is  like  the  mitral,  but  with  three  flaps 
instead  of  two, 

Semilunar  Valves. — These  are  six  in  number  ;  three  at 
the  mouth  of  the  aorta,  Fig.  59,  and  three,  quite  like  them, 
at  the  mouth  of  the  pulmonary  artery.  Each  is  a  strong 
crescentic  pouch  fixed  by  its  more  curved  border,  and  with 
its  free  edge  turned  away  from  the  heart.  When  the  valves 
are  in  action  their  free  edges  meet  across  the  vessel  and 
prevent  blood  from  flowing  back  into  the  ventricle. 

The  Course  of  the  Main  Arteries  of  the  Body  (Fig.  60). 
— The  aorta  after  leaving  the  left  ventricle  makes  an  arch 

What  is  found  between  each  auricle  and  ventricle?  What  are 
they  called?  Describe  the  mitral  valve.  Where  is  it  placed?  What 
are  the  chordae  tendineae?  The  papillary  muscles?  How  far  will 
the  cords  allow  the  valve  flaps  to  rise?  How  does  the  tricuspid  valve 
differ  from  the  mitral? 

How  many  semilunar  valves  are  there?  Where  are  they  placed? 
Describe  them.  What  is  their  use? 


202  2 HE    HUMAN   BODY. 

(«A)  with  its  convexity  towards  the  head.  From  the  heart 
end  of  this  arch  arise  the  coronary  arteries,  which  carry 
blood  into  the  walls  of  the  heart.  From  the  convexity  of 
the  arch  spring  the  three  large  trunks :  the  innominate 
artery  ;  the  left  common  carotid  artery  (cs) ;  and  the  left 
subclavian  artery  (ssi).  The  innominate  soon  divides  into 
the  right  subclavian  (sd),  and  the  right  common  carotid  (cd) 
Each  common  carotid  runs  up  the  neck  on  its  own  side, 
and  divides  into  branches  for  the  neck,  face,  scalp,  and  brain. 
Each  subclavian  continues  across  the  arm-pit  as  the  axil- 
lary artery  (ACC),  and  then  runs  down  to  near  the  elbow  as 
the  brachial  artery  (B).  Just  above  the  elbow  it  divides 
into  the  radial  and  ulnar  arteries  (R,  u,)  which  supply  the 
fore-arm,  and  end  in  small  brandies  for  the  hand 

Beyond  its  arch  the  aorta  runs  back  close  to  the  spinal 
column  as  the  thoracic  aorla  (A/),  which  gives  off  branches 
to  the  walls  of  the  chest  and  some  organs  in  that  cavity. 
The  vessel  then  passes  through  the  diaphragm,  and  con- 
tinues as  the  abdominal  aorta  (&ab)  to  the  lower  part  of  the 
abdomen.  The  main  branches  of  the  abdominal  aorta  are: 
(1)  the  cceliac  axis,  which  divides  into  branches  for  the 
stomach,  liver,  and  spleen;  (2)  the  upper  and  lower  mesen- 
teric  arteries,  which  supply  the  intestines  with  blood;  (3) 
the  renal  arteries  (K),  which  carry  blood  to  the  kidneys. 


What  is  meant  by  the  aortic  arch?  What  are  its  first  branches? 
What  branches  are  given  off  from  the  upper  side  of  the  aortic 
arch?  Into  what  vessels  does  the  innominate  artery  divide?  To 
•what  parts  do  the  common  carotid  arteries  carry  blood?  In  what 
does  the  subclavian  artery  terminate?  What  vessels  supply  the 
fore-arm  with  blood?  How  do  they  end? 

What  is  the  thoracic  aorta? 

The  abdominal  aorta?  Name  the  chief  branches  of  the  abdom- 
inal aorta.  What  organs  are  supplied  by  the  cceliac  axis?  The 
mesenteric  arteries?  The  renal  arteries? 


FIG.  60.— The  main  arteries  of  the  body.  Crd  and  Crs,  right  and  left  coronary 
arteries  of  the  heart,  cut  short  near  their  origin;  Aa,  and  aA,  aortic  arch;  At, 
thoracic  aorta;  Aab,  abdominal  aorta;  .K",  renal  artery;  Sd,  right,  and  8si,  left 
suhclavian:  Cd,  right,  and  Cs.  left  carotid;  Ax,  axillary  artery;  JS,  brachial 
artery;  U,  ulnar  artery;  R,  radial  artery;  Ai.  common  iliac  artery;  /.  external 
iliac  artery;  (?,  femoral  artery;  Po,  popliteal  artery;  Ta,  anterior,  and  Tp.  pos- 
terior tibial  artery ;  Pe,  peroneal  artery. 


204  THE  HUMAN  BODY. 

The  two  trunks  into  which  the  posterior  end  of  the  ab- 
dominal aorta  divides  (Ai)  are  named  the  common  iliac 
arteries ;  each  gives  off  some  branches  in  the  pelvis,  and 
then  continues  along  the  thigh  as  the  femoral  artery  (C)', 
this  runs  to  the  knee-joint,  behind  which  it  is  called  the 
popliteal  artery  (Po).  The  popliteal  artery  divides  into 
the  peroneal  (Pe)  and  tibial  (Ta,  Tp)  arteries,  which  sup- 
ply the  lower  leg  and  the  foot. 

The  Properties  of  the  Arteries. — Two  fundamental  facts 
must  be  borne  in  mind  in  connection  with  the  arteries  : 
Fir  si,  that  they  are  highly  elastic  and  extensible  ;  a  large 
artery  is,  in  this  respect,  much  like  a  piece  of  rubber  tub- 
ing of  the  same  size.  Second,  the  arteries  have  rings  of 
muscular  tissue  in  their  walls,  and  when  the  muscle  con- 
tracts the  bore  of  the  artery  (and  consequently  the  amount 
of  blood  which  flows  through  it)  is  diminished.  When  the 
muscle  relaxes,  the  bore  of  the  artery  is  increased,  and  more 
blood  passes  along  it  to  the  capillaries  in  which  it  ends. 

The  Capillaries. — The  smallest  arteries  pass  into  the 
capillaries,  which  have  very  thin  walls,  and  form  very  close 
networks  in  nearly  all  parts  of  the  body ;  their  immense 
number  compensating  for  their  smaller  size.  The  average 
diameter  of  a  capillary  vessel  is  so  small  that  only  two  or 
three  blood-corpuscles  can  pass  through  it  abreast,  and  in 
many  parts  the  capillaries  lie  so  close  together  that  a  pin's 

Into  what  vessels  does  the  abdominal  aorta  ultimately  divide? 
What  is  the  femoral  artery  derived  from?  To  what  point  does  it 
run?  What  is  the  popliteal  artery?  Into  what  branches  does  the 
popliteal  artery  divide?  What  parts  do  they  supply  with  blood? 

What  main  facts  are  to  be  borne  in  mind  in  connection  with  the 
arteries?  How  is  the  quantity  of  blood  which  an  artery  will  let  pass 
regulated? 

What  is  found  when  the  arteries  are  followed  to  the  ends  of  their 
smallest  branches?  Describe  the  structure,  arrangement  and  size  of 
the  capillaries. 


THE    VEINS.  205 

point  could  not  be  inserted  between  two  of  them,  as,  for 
instance,  in  the  deep  layers  of  the  skin  which  can  hardly 
be  pricked  anywhere  with  a  needle  without  drawing  blood. 
It  is  while  flowing  in  these  delicate  tubes  that  the  blood 
does  its  nutritive  work,  the  arteries  being  merely  supply- 
tubes  for  the  capillaries,  through  whose  delicate  walls 
liquid  containing  nourishment  exudes  from  the  blood  to 
bathe  the  various  tissues.  Imagine  a  piece  of  the  finest 
lace,  with  all  its  threads  consisting  of  hollow  tubes,  and 
diminished  twenty  times  in  size,  and  you  will  have  some 
idea  of  the  capillaries. 

The  Veins. — The  first  veins  arise  from  the  capillary  net- 
works in  various  organs,  and  like  the  last  arteries  are  very 
small.  They  soon  increase  in  size  by  union,  and  so  form 
larger  and  larger  trunks  alongside  the  main  artery  of  the 
part,  but  there  are  many  more  large  veins  just  beneath  the 
skin  than  there  are  large  arteries.  This  is  especially  the 
case  in  the  limbs,  the  main  veins  of  which  are  superficial, 
and  can  in  many  persons  be  seen  as  faint  blue  lines  through 
the  skin. 

Why  the  large  Arteries  usually  lie  deep. — The  heart 
pumps  the  blood  with  great  force  into  the  arteries,  and  if 
an  artery  is  cut  very  rapid  and  dangerous  bleeding  occurs ; 
the  veins,  if  cut,  do  not  bleed  nearly  so  violently  as  an 
artery  of  the  same  size.  Hence  it  is  less  dangerous  to  have 
a  large  vein  than  a  large  artery  close  under  the  skin. 

Point  out  a  fact  illustrating  the  closeness  of  the  capillaries  in 
many  parts  of  the  body.  What  does  the  blood  do  as  it  flows  through 
the  capillaries? 

Where  do  the  first  veins  arise?  What  is  their  size?  How  do 
they  increase  in  size?  Where  do  the  larger  veins  lie?  In  what  parts 
of  the  body  do  we  especially  find  large  veins  close  beneath  the  skin? 

Why  are  the  large  arteries,  as  a  rule,  placed  deeper  than  veins  of 
corresponding  size? 


206 


THE    HUMAN   BODY 


The  Valves  of  the  Veins.— Except  the  pulmonary  artery 
and  the  aorta,  which  have  the  semilunar  valves,  arteries  have 
no  valves.  Most  veins,  on  the  contrary,  contain  many  valves 
formed  by  pouches  of  their  lining,  which  resemble  in  form 
the  semilunar  valves  of  the  aorta  and  the  pulmonary  artery, 


FIG.  61.— A  small  portion  of  the  capillary  network  us  seen  in  the  frog's  web  when 
magnified  about  25  diameters,  a,  a  small  artery  feeding  the  capillaries;  v,  v,  small 
veins  carrying  blood  back  from  the  latter. 

What  arteries  have  valves?  Where  are  these  valves  placed? 
How  do  veins  differ  from  arteries  in  regard  to  the  presence  of  valves 
in  them? 


VALVES  OP  THE  VEINS.  207 

but  are  turned  in  the  opposite  direction,  having  the  edge 
nearest  the  heart  free  and  the  other  fixed.  These  valves 
permit  blood  to  flow  only  towards  the  heart,  for  a  current 
in  that  direction,  as  in  the  upper  diagram,  Fig.  6%, 
presses  the  valve  close  against  the  side  of  the  vessel,  and 
meets  with  no  obstruction  from  it.  Should  any  back-flow 
be  attempted,  however,  the  current  closes  up  the  valve  and 
bars  its  own  passage,  as  indicated  in  the  lower  figure. 
These  valves  are  most  numerous  in  superficial  veins  and 

those  of  muscular  parts.     Usually          _  

the  vein  is  a  little  dilated  opposite  >- 

a  valve,  and  hence  in  parts  where  '" 

the  valves   are   numerous   gets   a          _____ 

knotted   look.     On  tying  a  cord 
tightly  round  the  fore-arm,  so  as 

,  ,  ,  i  a  •  L  ix  FlG-  62.— Diagram  to  illus- 

to  Stop  the  nOW  in  its  SUDCUtaneOUS  trate  the  mode  of  action  of 

.,  .  , .,  .  .  .  the  valves  of  the  veins.  C,  the 

Veins  and  Cause  their  dilatation,  capillary,  H,  the  heart  end  of 

i-ii  the  vessel. 

the    points    at   which  valves  are 

placed  can  be  recognized  by  their  swollen  appearance.    The 

valves  are  most  frequently  found  where  two  veins  communi- 

cate0 

The  Course  of  the  Blood.— From  what  has  been  said  it 
is  cloar  that  the  movement  of  the  blood  is  a  circulation. 
Starting  from  any  one  chamber  of  the  heart  it  will  in  time 
return  to  it:  but  to  do  this  it  must  pass  through  at  least 
two  sets  of  capillaries;  one  of  these  is  connected  with  the 

In  what  direction  do  the  valves  of  the  veins  allow  the  blood 
to  pass?  Make  a  diagram  illustrating  the  action  of  the  valves. 
In  what  veins  are  the  valves  most  numerous?  Why  does  a  vein  with 
many  valves  appear  knotted?  How  may  we  see  the  dilatations  of 
the  veins  opposite  the  valves?  Where  are  the  valves  of  the  veins 
most  frequently  placed? 

If  we  followed  the  blood  course  steadily  from  one  chamber  of  the 
heart  what  would  we  find  in  time?  Through  what  must  blood  pass 
before  returning  to  the  chamber  of  the  heart  which  it  leaves? 


208  THE  SUM  AN  BODY. 

aorta,  and  the  other  with  the  pulmonary  artery,  and  in  its 
circuit  the  blood  returns  to  the  heart  twice.  Leaving  the 
left  side  it  returns  to  the  right,  and  leaving  the  right  it 
returns  to  the  left;  and  there  is  no  road  for  it  from  one 
side  of  the  heart  to  the  other  except  through  a  capillary 
network.  Moreover,  it  always  leaves  from  a  ventricle 
through  an  artery,  and  returns  to  an  auricle  through  a 
vein. 

There  is  then  really  only  one  circulation;  but  it  is  not 
uncommon  to  speak  of  two,  the  flow  from  the  left  side  of 
the  heart  to  the  right  through  most  of  the  body  being 
called  the  systemic  or  greater  circulation,  and  from  the 
right  to  the  left  through  the  lungs  the  pulmonary  or  lesser 
circulation.  But  since,  after  completing  either  of  these 
alone,  the-  blood  is  not  again  at  the  point  from  which  it 
started,  but  is  separated  frcm  it  by  the  septum  of  the 
heart,  neither  is  a  "circulation"  in  the  proper  sense  of  the 
word,  for  a  circulation  implies  that  any  object  at  the  end 
of  its  course  is  again  exactly  where  it  was  at  the  com- 
mencement. 

The  Portal  Circulation.— A  certain  portion  of  the  blood 
which  leaves  the  left  ventricle  of  the  heart  through  the 
aorta  has  to  pass  through  three  sets  of  capillaries  before  it 
can  again  return  there.  This  is  the  portion  which  goes 
through  the  stomach  and  intestines.  After  traversing  the 
capillaries  of  those  organs  it  is  collected  into  the  portal 

Through  what  does  blood  always  leave  the  heart?  To  what  does 
it  return?  How  many  circulation*  are  there  really?  What  is  meant 
by  the  systemic  circulation?  What  by  the  pulmonary?  Why  is 
neither  a  true  "  circulation"  in  the  proper  sense  of  the  word? 

How  many  sets  of  capillaries  does  some  blood  pass  through  in  a 
complete  circulation?  What  portion  of  the  blood  is  it?  What  vessel 
doec  it  enter  after  traversing  the  capillaries  of  the  stomach  and  in- 
testines? 


TEE  PORTAL  CIRCULATION. 


209 


vein,  which  enters  the  liver,  and  breaking  up  there  into 
finer  and  finer  branches  like  an  artery,  ends  in  the 
capillaries  of  that  organ,  forming 
the  second  set  which  this  blood 
passes  through  on  its  course. 
From  these  it  is  collected  by  the 
hepatic  veins,  which  pour  it  into 
the  inferior  vena  cava  which  car- 
ries it  to  the  right  auricle,  so  that 
it  has  still  to  pass  through  the 
pulmonary  capillaries  to  get  back 
to  the  left  side  of  the  heart.  The 
portal  vein  is  the  only  one  in  the 
human  body  which  thus  like  an 
artery  feeds  a  capillary  network, 
and  the  flow  from  the  stomach 
and  intestines  through  the  liver 
to  the  inferior  vena  cava,  is  often 
spoken  of  as  i\iQ  portal  circulation. 
Diagram  of  the  Circulation.— 
Since  the  two  halves  of  the  heart, 
although  placed  in  proximity  in 


FIG.  63  Diagram  of  the 
blood  vascular  system,  show- 
ing that  it  forms  a  single 
closed  circuit  with  two  pumps 
in  it,  represented  by  the  right 
and  left  halves  of  the  heart, 
which  are  separated  in  the 
diagram,  ra  and  rv,  right  aur^- 
cle  and  ventricle;  la  and  Zv, 


.,        .      ,  ,,  ,    .    ,         left  auricle  and  ventricle;  ao, 

the   body,    are   actually   Completely      aorta;    sc,    systemic   capilla- 
ries; vc,  venae  cavre;  pa,  pul- 

Separated  from    One    another  by  an      monary artery ;pc,pulmonary 

capillaries;    pv,    pulmonary 

impervious  partition,  we  may  con-     veins. 
veniently  represent  the  course  of  the  blood  as  in  the  ac- 
companying  diagram   (Fig.  63),  in  which  the  right  and 

Where  does  this  vein  carry  it?  In  what  does  it  end?  Into 
what  vessels  is  the  blood  of  the  capillaries  of  the  liver  collected? 
Where  do  they  convey  it?  What  chamber  of  the  heart  does  it 
first  reach?  Through  what  must  it  pass  to  get  back  to  the  left 
ventricle?  How  does  the  portal  vein  differ  from  all  others  in  the 
body?  What  is  meant  by  the  portal  circulation? 


210  THE  HUMAN  BOD  T. 

left  halves  of  the  heart  are  represented  at  different  points 
in  the  vascular  system.  Such  a  diagram  makes  it  clear  that 
the  heart  is  really  two  pumps  working  side  by  side,  and 
each  engaged  in  forcing  blood  to  the  other.  Starting  from 
the  left  auricle,  la,  and  following  the  flow,  we  trace  it 
through  the  left  ventricle,  and  along  the  branches  of 
the  aorta  into  the  systemic  capillaries,  sc;  thence  it 
passes  back  through  the  systemic  veins,  vc.  Reaching 
the  right  auricle,  ra,  it  is  sent  into  the  right  ventricle,  rv9 
and  thence  through  the  pulmonary  artery,  pa,  to  the  lung 
capillaries,  pc,  from  which  the  pulmonary  veins,  pv,  carry 
it  to  the  left  auricle,  which  drives  it  into  the  left  ventricle, 
Iv,  and  this  again  into  the  aorta. 

Arterial  and  Venous  Blood.— The  blood  when  flowing 
in  the  pulmonary  capillaries  gives  up  carbon  dioxide  (a 
waste  product  which  it  has  gathered  in  its  flow  through 
the  other  organs)  to  the  air,  and  receives  oxygen  from  it; 
since  its  coloring  matter  (hemoglobin)  forms  a  scarlet 
compound  with  oxygen,  the  blood  which  flows  to  the  left 
auricle  through  the  pulmonary  veins  is  of  a  bright  red 
color.  This  color  it  maintains  until  it  reaches  the  sys- 
temic capillaries,  but  in  these  it  loses  much  oxygen  to 
the  surrounding  tissues,  and  gains  much  carbon  dioxide 
from  them.  But  the  blood-coloring  matter  which  has  lost 
its  oxygen  has  a  dark  purple-black  color,  and  since  this 
unoxidized  or  "  reduced  "  haemoglobin  is  now  in  excess,  the 


Why  are  we  justified  in  diagraumratically  representing  the  heart 
as  made  of  two  separated  parts?  Starting  from  the  left  auricle, 
describe  the  course  of  the  blood  until  it  returns  there. 

What  does  the  blood  give  up  in  the  pulmonary  capillaries?  What 
does  it  receive?  Why  is  it  bright  red  when  it  enters  the  left  auricle? 
How  far  in  its  course  does  it  keep  this  color?  What  gases  does  the 
blood  gaiu  and  lose  in  the  ^  jjieiuiv;  capillaries? 


APPENDIX. 


blood  returns  to  the  right  auricle  of  the  heart  by  the 
venae  cavae  of  a  dark  purple-red  color.  This  color  it 
keeps  until  it  reaches  the  lungs,  where  the  reduced  haemo- 
globin becomes  again  oxidized.  The  bright  red  blood, 
rich  in  oxygen  and  poor  in  carbon  dioxide,  is  known  as 
"arterial  blood,"  and  the  dark  red  as  "  venous  blood;" 
and  it  must  be  borne  in  mind  that  the  terms  have  this 
peculiar  technical  meaning,  and  that  the.  pulmonary  veins 
contain  arterial  blood,  and  the  pulmonary  arteries  contain 
venous  blood.  The  change~~lfom  arterial  to  "venous  takes 
place  in  the  systemic  capillaries,  and  from  venous  to 
arterial  in  the  pulmonary  capillaries. 

What  color  is  the  blood  when  returned  to  the  right  auricle?  Why? 
What  is  meant  by  arterial  blood?  By  venous?  What  veins  contain 
arterial  blood?  What  arteries  venous?  Where  does  the  change 
from  arterial  to  venous  occur?  Where  that  from  venous  to  arterial? 


APPENDIX  TO  CHAPTER  XIV. 

1.  In  the  following  directions  "  dorsal "  means  the  side  of  the  heart 
naturally  turned  towards  the  vertebral  column,  "ventral"  the  side 
next  the  breast-bone;  "right"  and  "left"  refer  to  the  proper  right 
and  left  of  the  heart  when  in  its  natural  position  in  the  body;  "  an- 
terior" means  more  towards  the  head  in  the  natural  position  of  the 
parts;  and  "  posterior"  the  part  turneJ  away  from  the  head. 

2.  Get  your  butcher  to  obtain  for  you  a  sheep's  heart,  not  cut  out 
of  the  bag  (pericardium),  and  still  connected  with  the  lungs.     Impress 
upon  him  that  no  hole  must  be  punctured  in  the  heart,  such  as  is 
usually  made  when  a  slaughtered  sheep  is  cut  up  for  market. 

3.  Place  the  heart  and  lungs  on  their  dorsal  sides  on  a  table  in 
their  normal  relative  positions,  and  with  the  windpipe  directed  away 
from  you.     Note  the  loose  bag  (pericardium)  in  which  the  heart  lies, 
and  the  piece  of  midriff  (diaphragm)  which  usually  is  found  attached 
to  its  posterior  end. 

4.  Carefully  dissecting  aw.iv  adherent  fat,  etc.v  trace  the  vessels 


212  THE  HUMAN  BODY. 

below  named  until  they  enter  the  pericardium.  Be  very  careful  not 
to  cut  the  veins,  which,  being  thin,  collapse  when  empty,  and  may 
be  easily  overlooked  until  injured.  As  each  vein  is  found  stuff  it 
with  raw  cotton,  which  makes  its  dissection  much  easier. 

a.  The  vena  cava  inferior  :  find  it  on  the  under  (Abdominal)  side  of 
the  diaphragm ;  thence  follow  it  until  it  enters  the  pericardium,  about 
three  inches  further  up;  to  follow  it  in  this  part  of  its  course,  turn 
the  right  lung  towards  your  left  and  the  heart  towards  your  right. 

The  vein  just  below  the  diaphragm,  may  be  seen  to  receive  several 
large  vessels,  the  hepatic  veins. 

As  it  passes  through  the  midriff,  two  veins  from  that  organ  enter  it. 

Between  diaphragm  and  pericardium  the  inferior  cava  receives  no 
branch;  but,  lying  on  its  left  side,  will  be  seen  the  lower  end  of  the 
right  phrenic  nerve,  ending  below  in  several  branches  to  the  diaphragm. 

b.  Superior  vena  cava :  seek  its  lower  end,  entering  the  pericardium 
about  one  inch  above  the  entry  of  the  inferior  cava;  thence  trace  it 
up  to  the  point  where  it  has  been  cut  across;  stuff  and  clean  it. 

c.  Between  the  ends  of  the  two  venae  cavse  will  be  seen  the  two 
right  pulmonary  veins,  proceeding  from  the  lung  and  entering  the 
pericardium;  clean  and  stuff  them. 

5.  Turn  the  right  lung  and  the  heart  back  into  their  natural  posi- 
tions; clear  away  the  loose  fat  in  front  of  the  pericardium,  and  seek 
and  clean  the  following  vessels  in  the  mass  of  tissue  lying  anterior  to 
the  heart,  and  on  the  ventral  side  of  the  windpipe. 

a.  The  aorta  :  immediately  on  leaving  the  pericardium  this  vessel 
gives  off  a  large  branch;  it  then  arches  back  and  runs  down  behind 
the  heart  and  lungs,  giving  off  several  branches  on  its  way. 

6.  The  pulmonary  artery  :  this  will  be  found  imbedded  in  fat  on 
the  dorsal  side  of  the  aorta.     After  a  course,  outside  the  pericardium, 
of  about  an  inch,  it  ends  by  dividing  into  two  large  branches  (right 
and  left  pulmonary  arteries),  which  subdivide  into  smaller  vessels  as 
they  enter  the  lungs. 

c.  Observe  the  thickness  and  firmness  of  the  arterial  walls  as 
compared  with  those  of  the  veins;  they  stand  out  without  being 
stuffed. 

6.  Notice,  on  the  ventral  side  of  the  left  pulmonary  artery,  the 
left  pulmonary  veins  passing  from  the  lung  into  the  pericardium. 

7.  Up  to  this  point  the  dissection  may  be  made  before  the  meeting 
of  the  class;    on  the  preparation  demonstrate  the  anatomical  facts 
above  noted  and  then  proceed  as  follows: 

8.  Slit  open  the  pericardiac  bag,  and  note  its  smooth,  moist,  glis- 
tening inner  surface,  and  the  similar  character  of  the  outer  surface  of 
the  heart.     Cut  away  the  pericardium  carefully  from  the  entrances 
of  the  various  vessels  which  you  have  already  traced  to  it.     As  this 


APPENDIX.  213 

is  done,  you  will  notice  that  inside  the  pericardium  the  pulmonary 
artery  lies  on  the  ventral  side  of  the  aorta. 

9.  Note  the  general  form  of  the  heart — that  of  a  cone  with  its  apex 
turned  towards  the  diaphragm.     Very  carefully  dissect  out  the  entry 
of  the  pulmonary  veins  into  the  heart.     It  will  probably  seem  as  if 
the  right  pulmonary  veins  and  the  inferior  cava  opened  into  the  same 
portion  of  the  organ,  but  it  will  be  found  subsequently  (13.  a.)  that  such 
is  not  really  the  case.    Note  on  the  exterior  of  the  organ  the  follow- 
ing points: 

a.  Its  upper  flabby  auricular  portion  into  which  the  veins  open, 
and  its  denser  lower  ventricular  part. 

b.  Running  around  the  top  of  the  ventricles  is  a  band  of  fat,  an 
offshoot  of  which  runs  obliquely  down  the  front  of  the  heart,  passing 
to  the  right  of  its  apex,  and  indicating  externally  the  position  of  the 
internal  partition   or  septum  which   separates    the  right   ventricle, 
which  does  not  reach  the  apex  of  the  heart,  from  the  left,  which 
does. 

c.  Note  the  fleshy  "  auricular  appendages" — one  (left)  appearing 
below  the  pulmonary  artery;  the  other  (right),  between  the  aorta  and 
superior  cava. 

10.  Dissect  away  very  carefully  the  collection  of  fat  around  the 
origins  of  the  great  arterial  trunks  and  that  around  the  base  of  the 
ventricles.     In  the  fat  will  be  found — 

a.  A  coronary  artery  arising  from  the  aorta  close  to  the  heart, 
opposite  the  right  border  of  the  pulmonary  artery;  it  gives  off  a 
branch  which  runs  in  the  groove  between  right  auricle  and  ventricle, 
and  then  runs  down  the  dorsal  side  of  the  heart  on  the  ventricles. 

b.  The  other  coronary  artery,  considerably  larger,  arises  from  the 
aorta  dorsal  to  the  pulmonary  artery;  its  main  branch  runs  along 
the  ventral  edge  of  the  ventricular  septum. 

c.  The  coronary  wins  and  sinus:  small  coronary  veins  will  be 
seen  accompanying  the  arteries;  for  the  coronary  sinus  see  11.  c. 

11.  Open  the  right  ventricle  by  passing  the  blade  of  a  scalpel 
through  the  heart  about  an  inch  from  the  upper  border  of  the  ventri- 
cle, and  on  the  right  of  the  band  of  fat  marking  externally  the  limits 
of  the  ventricles,  and  noted  above  (9.  &.).  and  then  cut  down  towards 
the  apex,  keeping  on  the  right  of  this  line;  cut  off  the  pulmonary 
artery  about  an  inch  above  Its  origin  from  the  lieart,  and  open  the 
right  auricle  by  cutting  a  bit  cut  of  its  wall,  to  the  left  of  the 
entrances  of  the  venaa  cavse.     On  raising  up  by  its  point  the  wedge- 
shaped  flap  cut  ^rom  the  wall  of  the  ventricle,  the  cavity  of  the  latter 
will  be  exposed. 

a.  Pass  the  handle  of  a  sca\pei  from  the  ventricle  into  the  auricle; 


214  THE  HUMAN  BODY. 

» 

and  also  from  the  ventricle  into  the  pulmonary  artery,  and  make  out 
thoroughly  the  relations  of  these  openings. 

b.  Slit  open  the  auricular  appendage;  note  the  fleshy  projections 
(columncB  carnece)  on  it's  walls,  and  the  smoothness  of  the  rest  of  the 
interior  of  the  auricle.      Observe  the  apertures  of  the  vence  caves, 
and  note  that  the  pulmonary  veins  do  not  open  into  this  auricle. 

c.  Behind  or  below  the  entrance  of  the  inferior  cava,  note  the 
entrance  of  the  coronary  sinus;  pass  a  probe  through  the  aperture 
along  the  sinus  and  slit  it  open ;  notice  the  muscular  layer  covering 
it  in. 

12.  Raise  up  by  its  apex  the  flap  cut  out  of  the  ventricular  wall, 
and  if  necessary  prolong  the  cuts  more  towards  the  base  of  the  ven- 
tricle until  the  divisions  of  the  tricuspid  valve  come  into  view. 

a.  Note  the  columns  carneae  on  the  wall  of  the  ventricle,  and  the 
muscular  cord  (not  found  in  the  human  heart)  stretching  across  its 
cavity.     Also  the  prolongation  of  the  ventricular  cavity  towards  the 
aperture  of  the  pulmonary  artery. 

b.  Cut  away  the  right  auricle,  and  examine  carefully  the  tricuspid 
valve,  composed  of  three  membranous  flexible  flaps,  thinning  away 
towards  their  free  edges;  proceeding  from  near  these  edges  are  strong 
tendinous  cords  (chorda  tendinece),  which  are  attached  at  their  other  ends 
to  muscular  elevations  (papillary  muscles)  of  the  wall  of  the  ventricle. 

c.  Slit  up  the  right  ventricle  until  the  origin  of  the  pulmonary 
artery  comes  into  view.     Looking  carefully  for  the  flaps  of  the  semi- 
lunar  valves,  prolong  your  cut  between  two  of  them  so  as  to  open  the 
bit  of  pulmonary  artery  still  attached  to  the  heart.  •  Spread  out  the 
artery  and  examine  the  valves. 

d.  Each  flap  makes,  with  the  wall  of  the  artery,  a  pouch,  opposite 
which  the  arterial  wall  is  slightly  dilated.     The  free  edge  of  the 
valve  is  tumed  from  the  heart,  and  has  in  its  middle  a  little  nodule 
(corpus  Arantiij. 

13.  Open  the  left  ventricle  in  a  manner  similar  to  that  employed 
for  the  right.     Then  open  the  left  auricle  by  cutting  a  bit  out  of  its 
wall  above  the  appendage.     Cut  the  aorta  off  about  half  an  inch 
above  its  origin  from  the  heart.     The  aperture  between  left  auricle 
and  left  ventricle  can  now  be  examined;  also  the  passage  from  the 
ventricle  into  the  aorta,  and  the  entry  of  the  pulmonary  veins  into 
the  auricle;  and  the  septum  between  the  auricles  and  that  between 
the  ventricles. 

a.  Pass  the  handle  of  a  scalpel  from  the  ventricle  into  the  auricle; 
another  from  the  ventricle  into  the  aorta;  and  pass  also  probes  into 
the  points  of  entrance  of  the  puknonary  veins.  Observe  that  no  other 
veins  open  into  this  auricle. 


APPENDIX.  £15 

5.  Slit  open  the  auricular  appendage;  note  the  fleshy  projections 
(columnce  carnece)  on  its  interior,  and  the  general  smoothness  of  the 
rest  of  the  inner  wall  of  the  auricle.  Notice  the  columna  carnecs 
over  the  inner  surface  of  the  ventricular  wall,  also  the  considerable 
thickness  of  the  latter,  as  compared  with  that  of  the  right  ventricle  or 
of  either  of  the  auricles. 

c.  Carefully  raise  the  wedge-shaped  flap  of  the  left  ventricle,  and 
cut  on  towards  the  base  of  the  heart,  until  the  valve  (mitral)  between 
auricle  and  ventricle  is  brought  into  view;  one  of  its  two  flaps  will 
be  seen  to  lie  between  the  auriculo-ventricular  opening  and  the  origin 
of  the  aorta. 

Examine  in  these  flaps  their  texture,  the  chordae  tendineee,  the 
columnae  carnese,  etc.,  as  in  the  case  of  the  right  side  of  the  heart  (12). 

d.  Examine  the  semilunar  valves  at  the  exit  of  the  aorta;  then 
cutting  up  carefully  between  two  of  them,  examine  the  bit  of  aorta 
still  left  attached  to  the  heart,  and  note  the  valves  more  carefully  as 
described  in  12.  d.     Note  the  origins  of  the  coronary  arteries  in  two 
of  the  three  dilatations  (sinuses  of  Valsalva)  of  the  aortic  wall  above 
the  semilunar  flaps. 

14.  Examine  a  piece  of  aorta.     Note  that  when  empty  it  does  not 
collapse;  the  thickness  of  its  wall ;  its  extensibility  in  all  directions; 
its  elasticity. 

15.  Compare  with  the  artery  the  thin-walled  flabby  veins  which 
open  into  the  heart. 


CHAPTER  XV. 
THE  WORKING  OF  THE  HEART  AND  BLOOD-VESSELS. 

The  Beat  of  the  Heart. — It  is  possible  by  methods  known 
to  physiologists  to  open  the  chest  of  a  living  animal,  such 
as  a  rabbit,  made  insensible  by  chloroform,  and  see  its 
heart  at  work,  alternately  contracting  and  diminishing  the 
cavities  within  it,  and  relaxing  and  expanding  them.  It  is 
then  observed  that  each  beat  commences  at  the  mouths  of 
the  veins  which  open  into  the  auricles;  and  from  there  runs 
over  the  rest  of  the  auricles,  and  then  over  the  ventricles; 
the  auricles  beginning  to  dilate  the  moment  the  ventricles 
start  their  contraction.  Having  finished  their  contraction, 
the  ventricles  begin  to  dilate,  and  then  for  some  time 
neither  they  nor  the  auricles  are  contracting,  but  the 
whole  heart  is  expanding.  The  contraction  of  any  part  of 
the  heart  is  known  as  its  sys'to-le,  and  the  relaxation  as  its 
di-as'to-le,  and  since  the  two  sides  of  the  heart  work  syn- 
chronously, the  auricles  together  and  the  ventricles  to- 
gether, we  may  describe  a  whole  "  cardiac  period "  or 
"heart-beat"  as  made  up  successively  of  auricular  systole, 
ventricular  systole,  and  pause.  In  the  pause  the  heart,  if 
taken  between  the  finger  and  thumb  feels  soft  and  flabby, 

What  is  seen  when  the  beating  heart  of  a  living  animal  is  exposed? 
When  do  the  auricles  begin  to  dilate?  What  is  the  state  of  the  heart 
for  a  short  time  after  the  end  of  a  ventricular  contraction?  What  is 
meant  by  the  systole  of  apart  of  the  heart?  What  by  the  diastole?  Of 
•what  does  a  cardiac  period  consist?  How  does  the  heart  feel  to  the 
touch  during  the  pause? 

[216] 


EVENTS  DURING  A  CARDIAC  PERIOD.  217 

but  during  the  systole  it,  especially  in  its  ventricular  por- 
tion, becomes  hard  and  rigid,  and  diminished  in  size  so  as 
to  force  blood  out  of  it.  < 

The  Cardiac  Impulse. — The  human  heart  lies  with  its 
apex  touching  the  chest-wall  between  the  fifth  and  sixth 
ribs  on  the  left  side  of  the  breast-bone.  At  every  beat  a 
sort  of  tap  known  as  the  "cardiac  impulse,"  or  "apex 
beat,"  may  be  felt  by  placing  the  finger  at  that  point. 

Events  occurring  within  the  Heart  during  a  Cardiac 
Period. — Let  us  commence  just  after  the  end  of  the  ventric- 
ular systole.  At  this  moment  the  semilunar  valves  at  the 
orifices  of  the  aorta  and  the  pulmonary  artery  are  closed  so 
that  no  blood  can  flow  back  from  those  vessels.  The  whole 
heart,  however,  is  soft  and  distensible,  and  yields  readily  to 
blood  flowing  into  its  auricles  from  the  pulmonary  veins 
and  the  hollow  veins;  this  blood  passes  on  through  the  open 
mitral  and  tricuspid  valves,  and  fills  up  the  dilating  ventri- 
cles as  well  as  the  auricles.  As  the  ventricles  fill,  back  cur- 
rents are  set  up  along  their  walls,  and  carry  up  the  flaps 
of  the  auriculo-ventricular  valves,  so  that  by  the  end  of  the 
pause  they  are  nearly  closed.  At  this  moment  the  auricles 
contract;  this  contraction  commences  at  and  narrows  the 
mouths  of  the  veins  so  that  blood  cannot  easily  flow  back 
from  the  auricles  into  them;  the  flabby  and  dilating  ventri- 
cles oppose  much  less  resistance,  and  so  the  general  result  is 

How  (luring  the  systole?    How  is  its  bulk  changed  in  systole? 

Where  does  the  apex  of  the  heart  touch  the  chest- wall?  What  13 
the  cardiac  impulse? 

Wha'i  is  the  position  of  the  semilunar  valves  just  after  the  end  of 
a  ventricular  systole?  What  results  from  their  closure?  In  what 
condition  is  the  heart  in  general?  What  parts  of  it  does  blood  enter? 
From  what  vessels?  What  cavities  does  this  blood  till?  What  hap- 
pens as  the  ventricles  fill?  What  is  the  position  of  the  valves  at  the 
end  of  the  pause?  Where  does  the  auricular  contraction  commence? 
What  is  the  main  result  of  the  auricular  contraction? 


218  TEE  HUMAN  BODY. 

that  the  contracting  auricles  send  blood  mainly  into  the 
ventricles  and  hardly  any  back  into  the  veins.  The  in- 
creased current  into  the  ventricles  produces  a  greater  back 
current  on  the  sides,  which,  as  the  auricles  cease  their  con- 
traction, and  the  filled  ventricles  become  tense  and  press  on 
the  blood  inside  them,  completely  closes  the  auriculo-ven- 
tricular  valves. 

The  auricular  contraction  now  ceases,  and  the  ventricu- 
lar begins.  The  blood  in  each  ventricle  is  imprisoned  be- 
tween the  auriculo-ventricular  valves  behind  and  the  semi- 
lunar  valves  in  front.  The  former  cannot  yield  on  account 
of  the  chordaB  tendineae  fixed  to  their  edges;  the  semilunar 
valves,  on  the  other  hand,  can  open  outwards  from  the  ven- 
tricle and  let  the  blood  pass  on;  but  they  are  kept  tightly 
shut  by  the  pressure  of  the  blood  in  the  aorta  and  pulmo- 
nary artery,  just  as  the  lock-gates  of  a  canal  are  by  the  pres- 
sure of  the  water  on  them.  In  order  to  open  the  canal-gates 
water  is  let  in  or  out  of  the  lock  until  it  stands  at  the  same 
level  on  each  side  of  them;  but  they  might  be  forced  open 
without  this  by  applying  sufficient  power  to  overcome  the 
higher  water  pressure  on  one  side.  It  is  in  this  latter  way 
that  the  semilunar  valves  are  opened. 

The  contracting  ventricle  tightens  its  grip  on  the  blood 
inside  it.  As  it  squeezes  harder  and  harder,  at  last  the 
pressure  on  the  blood  in  it  becomes  greater  than  the  pres- 
sure exerted  on  the  other  side  of  the  valves  by  the  blood  in 


What  is  the  consequence  of  the  increased  flow  into  the  ventricles 
due  to  the  auricular  contraction? 

What  happens  when  the  ventricle  begins  to  contract?  Why  can- 
not the  imprisoned  blood  escape  back  into  the  auricle?  How  are  the 
semilunar  valves  kept  closed?  Illustrate.  How  might  we  force  open 
the  gates  of  a  canal  lock  without  bringing  the  water  to  the  same  level 
on  each  side? 

"'How  are  the  semilunar  valves  opened? 


USE  OF  PAPILLARY  MUSCLES.  219 

the  arteries,  the  valves  are  forced  open,  and  the  blood  begins 
to  pass  out;  the  ventricle  continues  to  contract  until  it  has 
obliterated  its  cavity  and  completely  emptied  itself.  Then 
it  commences  to  relax,  and  blood  to  flow  back  into  it  from 
the  arteries.  This  back  current,  however,  catches  the  pock- 
ets of  the  semilunar  valves,  drives  them  back,  and  closes  the 
valve  so  as  to  form  an  impassable  barrier,  and  so  the  blood 
which  has  been  forced  out  of  the  ventricle  is  hindered  from 
flowing  directly  back  into  it. 

Use  of  the  Papillary  Muscles, — In  order  that  the  con- 
tracting ventricles  may  not  force  blood  back  into  the  auri- 
cles, it  is  essential  that  the  flaps  of  the  mitral  and  tricuspid 
valves  be  held  together  across  the  openings  which  they 
close,  and  not  pushed  back  into  the  auricles.  If  they 
were  like  swinging  doors  and  opened  both  ways  they 
would  be  useless  ;  they  must  so  far  resemble  an  ordi- 
nary door  as  only  to  open  in  one  direction,  namely,  from 
the  auricle  to  the  ventricle.  At  the  commencement  of  the 
ventricular  systole  this  is  provided  for  by  the  chordae  tendin- 
eas,  which  are  of  such  a  length  and  so  arranged  as  to  keep 
the  valve-flaps  shut  across  the  opening,  and  to  maintain 
their  edges  in  contact.  But,  as  the  contracting  ventricles 
shorten,  the  chordae  tendineae  would  be  slackened  and  the 
valve-flaps  pushed  up  into  the  auricle.  The  little  papil- 
lary muscles  prevent  this.  Shortening  as  the  ventricular 
systole  proceeds,  they  keep  the  chordae  taut  and  the  valves 
closed. 

What  then  happens?  How  long  does  the  ventricle  continue  to 
contract?  What  then  follows?  How  are  the  semilunar  valves  closed? 

What  is  essential  In  order  that  blood  may  not  be  forced  back  from 
ventricle  to  auricle?  Illustrate.  How  is  the  pushing  back  of  the 
valve-flaps  between  auricle  and  ventricle  prevented  at  the  beginning 
of  a  ventricular  systole?  When  would  the  chordae  tendineae  be  slack- 
ened? What  would  result?  How  is  the  slackening  prevented? 


220  THE  HUMAN  BODY. 

Sounds  of  the  Heart. — If  the  ear  be  placed  on  the  chest 
of  another  person  over  the  heart  region,  two  distinguisha- 
ble sounds  will  be  heard  during  each  round  of  the  heart's 
work.  They  are  known  respectively  as  the  first  and  second 
sounds  of  the  heart.  The  first  is  of  lower  pitch  and  lasts 
longer  than  the  second  and  sharper  sound;  vocally  their 
character  may  be  tolerably  imitated  by  the  syllables  lul>,  dup. 
The  cause  of  the  second  sound  is  the  closure,  or,  as  one 
might  say,  the  "clicking  up"  of  the  semilunar  valves. 
The  first  sound  takes  place  during  the  ventricular  sys- 
tole, and  is  probably  due  to  vibrations  of  the  tense  ven- 
tricular wall  at  that  time.  In  many  forms  of  heart  disease 
these  sounds  are  modified  or  cloaked  by  additional  sounds 
which  arise  when  the  cardiac  orifices  are  roughened,  or  nar- 
rowed, or  dilated,  or  the  valves  inefficient.  A  physician 
often  gets  important  information  as  to  the  nature  of  a  heart 
disease  by  studying  these  new  or  altered  sounds. 

Function  of  the  Auricles. — The  ventricles  have  to  do  the 
work  of  pumping  the  blood  through  the  blood-vessels. 
Accordingly  their  walls  are  far  thicker  and  more  muscular 
than  those  of  the  auricles;  and  the  left  ventricle,  which  has 
to  force  the  blood  over  most  of  the  body,  is  stouter  than  the 
right,  which  has  only  to  send  blood  around  the  compara- 
tively short  pulmonary  circuit.  The  circulation  of  the 
blood  is,  in  fact,  maintained  by  the  ventricles,  and  we  have 
to  inquire  what  is  the  use  ol^Rie  auricles.  Not  unfre- 

What  do  we  hear  on  listening  over  the  heart  region  of  a  living  per- 
son's chest?  What  are  the  sounds  called?  How  does  the  first  differ 
from  the  second?  What  words  give  some  idea  of  their  character? 
What  is  the  origin  of  the  second  sound?  Of  the  first?  What  occurs 
as  regards  the  heart  sounds  in  many  forms  of  heart  disease? 

What  work  have  the  ventricles  to  do?  How  do  their  walls  differ 
from  those  of  the  auricles?  Which  ventricle  has  the  thicker  wall? 
Why?  What  part  of  the  heart  maintains  the  blood  flow? 


WORK  DONE  BY  THE  HEART.  221 

quently  the  heart's  action  is  described  as  if  the  auricles 
first  filled  with  blood,  and  then  contracted  and  filled  the 
ventricles;  and  then  the  ventricles  contracted  and  drove  the 
blood  into  the  arteries.  Erom  the  account  given  above, 
however,  it  will  be  seen  that  the  events  are  not  accurately 
so  represented,  but  that  during  all  the  pause  the  blood 
flows  on  through  the  auricles  into  the  ventricles,  which 
latter  are  already  nearly  full  when  the  auricles  contract; 
this  contraction  merely  completes  the  filling  of  the  ventri- 
cles, and  finishes  the  closure  of  the  auriculo-ventricular 
valves.  The  main  use  of  the  auricles  is  to  afford  a  reservoir 
into  which  the  veins  may  empty  while  the  comparatively 
long-lasting  ventricular  contraction  is  taking  place. 

The  Work  done  daily  by  the  Heart. — At  each  beat  each 
ventricle  pumps  on  rather  more  than  six  ounces  (say  four- 
teen tablespoonfuls)  of  blood.  The  elastic  aorta  and  the 
pulmonary  artery  are  full,  and  resist  the  pumping  of  more 
liquid  into  them,  just  as  an  elastic  bag  filled  with  water 
could  only  have  more  sent  into  it  by  force;  to  get  more  in 
one  would  have  to  stretch  the  bag  more.  The  resistance 
opposed  by  these  arteries  to  receiving  blood  from  the  heart 
has  been  measured  in  some  of  the  lower  animals,  and  calcu- 
lations made  from  them  to  man.  According  to  these  the 
work  which  the  left  ventricle  does  every  day,  sending  6J 
ounces  of  blood  seventy  times  a  minute  into  the  aorta,  is 
enough  to  lift  one  poundtS$5,584  feet  high;  and  the  work 
done  by  the  right  ventricle  would  lift  one  pound  108,528 

What  parts  of  the  heart  does  the  blood  enter  during  the  pause? 
What  is  the  condition  of  the  ventricles  as  regards  fullness  at  the 
end  of  the  pause?  What  is  done  by  the  auricular  contraction? 
What  is  the  chief  use  of  the  auricles? 

How  much  blood  does  each  ventricle  pump  out  at  every  beat? 
What  resists  the  ventricular  emptying?  Illustrate.  How  much 
work  does  a  man's  left  ventricle  do  daily?  How  much  the  right? 


222  'THE  HUMAN  BOLT. 

feet.  The  work  done  daily  by  the  ventricles  of  the  heart 
together  is  equal  to  that  required  to  raise  one  pound  434,112 
feet  from  the  earth's  surface,  or,  what  comes  to  the  same 
thing,  more  than  193  tons  one  foot  high. 

If  a  man  weighing  165  pounds  climbed  up  a  mountain 
2644  feet  high  the  muscles  of  his  legs  would  probably  be 
greatly  tired  at  the  end  of  his  journey,,  and  yet  in  lifting 
his  body  that  height  they  would  only  have  done  as  much 
work  as  his  heart  does  every  day  without  fatigue  in  pump- 
ing his  blood. 

No  doubt  the  fact  that  more  than  half  of  every  round 
of  the  heart's  activity  is  taken  up  by  the  pause  during 
which  its  muscles  are  relaxed  and  its  cavities  filling  with 
blood,  has  a  great  deal  to  do  with  the  patient  and  tireless 
manner  in  which  it  pumps  along,  minute  after  minute, 
hour  after  hour,  and  day  after  day,  from  birth  to  death. 

The  Pulse, — When  the  left  ventricle  of  the  heart  con- 
tracts it  forces  on  about  six  ounces  of  blood  into  the  aorta, 
which,  with  its  branches,  is  already  quite  full  of  blood. 
The  elastic  arteries  are  consequently  stretched  by  the  extra 
blood,  and  the  finger  laid  on  one  feels  it  dilating;  this  dila- 
tation of  an  artery  following  each  beat  of  the  heart  is  called 
the  pulse;  it  is  easiest  felt  on  arteries  which  lie  near  the 
surface  of  the  body,  as  the  radial  artery,  near  the  wrist, 
and  the  temporal  artery,  on  the  brow. 

The  arteries  at  their  ends  furthest  from  the  heart  lead 


How  much  both  ventricles  together? 

How  high  would  a  man  have  to  climb  in  order  to  do  as  much 
work  by  the  muscles  of  his  legs  as  the  heart  does  in  a  day? 

How  may  we  account  for  the  fact  that  the  heart  does  not  become 
fatigued  and  unable  to  work? 

What  happens  when  the  left  ventricle  of  the  heart  contracts? 
What  results  in  the  arteries?  What  is  the  pulse?  Name  arteries  or 
which  the  pulse  is  easily  felt. 


THE  PULSE.  223 

into  capillaries;  before  the  next  heart-beat  occurs  they  pass 
on  into  these  minute  vessels  as  much  blood  as  the  aorta  re- 
ceived during  the  preceding  ventricular  systole;  consequently 
they  shrink  again  during  the  pause,  just  as  a  piece  of  rubber 
tubing  with  a  small  hole  in  it,  when  overfilled  with  water, 
would  gradually  collapse  as  the  water  flowed  out  of  it.  The 
next  beat  of  the  heart  again  overfills  and  expands  the  arteries, 
and  so  on;  at  each  heart-beat  there  is  a  dilatation  of  the 
arteries  due  to  the  blood  sent  into  them  from  the  ventricle, 
and  between  each  beat  there  is  a  partial  collapse  of  the  ar- 
teries, due  to  their  emptying  blood  into  the  capillaries. 

What  may  be  learnt  from  the  Pulse, — The  pulse  being 
dependent  on  the  heart's  systole,  "feeling  the  pulse"  of 
course  primarily  gives  a  convenient  means  of  counting  the 
rate  of  beat  of  that  organ.  To  the  skilled  touch,  however, 
it  may  tell  a  great  deal  more;  as,  for  example,  whether  it  is 
a  readily  compressible  or  "soft  pulse,"  showing  that  the 
heart  is  not  keeping  the  arteries  properly  filled  up  with 
blood,  or  tense  and  rigid  ("a  hard  pulse"),  indicating  that 
the  heart  is  keeping  the  arteries  excessively  filled,  and  is 
working  too  violently,  and  so  on.  In  healthy  adults  the 
pulse  rate  may  vary  from  sixty-five  to  seventy-five  a  minute, 
the  most  common  rate  being  seventy-two.  In  the  same  in- 
dividual it  is  faster  when  standing  than  when  sitting,  and 
when  sitting  than  when  lying  down.  Any  exercise  in- 

Into  what  do  the  final  arterial  branches  open?  How  much  blood 
is  sent  into  the  capillaries  during  a  cardiac  period?  What  change 
takes  place  in  the  bulk  of  the  arteries  during  the  interval  between 
two  ventricular  contractions?  Illustrate.  What  happens  in  the 
arteries  during  each  heart-beat?  Why?  What  during  each  heart 
pause?  Why? 

How  may  we  conveniently  count  the  rate  of  heart-beat?  What 
does  a  soft  pulse  indicate?  A  hard  pulse?  What  is  the  most  com- 
mon pulse  rate  in  health?  Within  what  limits  may  it  vary?  How  is 
it  influenced  by  the  positbn  of  the  body? 


THE  HUMAN  BOLT. 


creases  its  rate  temporarily  and  so  does  excitement;  a  sick 
person's  pulse  should  not  therefore  be  felt  when  he  is  ner- 
vous or  excited  (as  the  physician  knows  when  he  tries  first 
to  get  his  patient  calm  and  confident).  In  children  the 
pulse  is  quicker  than  in  adults,  and  in  old  age  slower  than 
in  middle  life. 

The  Flow  of  the  Blood  in  the  Capillaries  and  Veins.  —  The 
blood  leaves  the  heart  intermittently  and  not  in  a  regular 
stream,  a  quantity  being  forced  out  at  each  systole  of  the 
ventricles;  before  it  reaches  the  capillaries,  however,  this 
rhythmic  movement  is  transformed  into  a  steady  flow,  as 
may  readily  be  seen  by  examining  with  a  microscope  thin 
transparent  parts  of  various  animals,  as  the  web  of  a  frog's 
foot,  a  bat's  wing,  or  the  tail  of  a  small  fish.  In  consequence 
of  the  steadiness  with  which  the  capillaries  supply  the  veins 
the  flow  in  these  latter  is  also  unaffected  directly  by  each 
beat  of  the  heart;  if  a  vein  be  cut  the  blood  wells  out  uni- 
formly, while  a  cut  artery  spurts  out  with  much  more  force, 
and  in  jets  which  are  more  powerful  at  regular  intervals 
corresponding  with  the  contractions  of  the  ventricles. 

The  Circulation  of  the  Blood  as  seen  in  the  Frog's 
Web,  —  There  is  no  more  fascinating  or  instructive  spectacle 
than  the  circulation  of  the  blood  as  seen  with  the  micro- 
scope in  the  thin  membrane  between  the  toes  of  a  frog's 
hind  limb.  Upon  focusing  beneath  the  outer  layer  of  the 
skin  a  network  of  minute  arteries,  veins,  and  capillaries, 

How  by  exercise?  Why  should  an  invalid's  pulse  not  be  felt 
when  he  is  excited?  How  does  age  affect  the  pulse  rate? 

In  what  manner  does  th-3  blood  leave  the  heart?  How  is  its  flow 
altered  before  reaching  the  capillaries?  How  may  this  be  observed? 
Is  the  flow  in  the  veins  rhythmic  or  steady?  Why?  How  does  the 
bleeding  from  a  cut  artery  differ  from  that  of  a  cut  vein? 

What  comes  into  view  on  examining  a  frog's  web  with  a  micro- 
scope? 


BLOOD  FLOW  IN  THE  CAPILLARIES.  225 

with  the  blood  flowing  through  them,  comes  into  view 
(Fig.  61).  The  arteries,  a,  are  readily  recognized  by  the 
fact  that  the  flow  in  them  is  Jastest  and  from  larger  to 
smaller  branches.  The  smallest  are  seen  to  end  in  capillar- 
ies, which  form  networks,  the  channels  of  which  are  all . 
nearly  equal  in  size.  In  the  veins  arising  from  the  capil- 
laries the  flow  is  from  smaller  to  larger  trunks,  and  slower 
than  in  the  arteries,  but  faster  than  in  the  capillaries. 

Why  the  Blood  flows  slowest  in  the  Capillaries. — The 
reason  of  the  slower  flow  of  £he  capillaries  is  that  their 
united  area  is  considerably  greater  than  that  of  the  arteries 
supplying  them,  so  that  the  same  quantity  of  blood  flowing 
through  them  in  a  given  time  has  a  wider  channel  to  flow 
in  and  therefore  moves  more  slowly.  The  area  of  the  veins 
is  smaller  than  that  of  all  the  capillaries,  but  greater  than 
that  of  the  arteries,  and  so  the  rate  of  movement  in  them  is 
intermediate. 

We  may  picture  to  ourselves  the  vascular  system  as  a 
double  cone,  widening  from  the  ventricles  to  the  capillaries, 
and  narrowing  from  the  latter  to  the  auricles.  Just  as 
water  forced  in  at  a  narrow  end  of  this  would  flow  quickest 
there,  slowest  at  the  widest  part,  and  quicker  again  where 
it  passed  out  the  other  narrow  end,  so  the  blood  flows  quick 
in  the  aorta  and  hollow  veins,*  and  slow  in  the  capillaries, 

How  may  the  arteries  be  recognized?  In  what  are  the  smallest 
arteries  seen  to  end?  Do  the  capillaries  vary  much  in  size?  What 
is  the  direction  of  flow  in  the  veins?  How  does  its  rate  differ 
from  that  in  the  arteries?  From  that  in  the  capillaries? 

Why  does  blood  flow  slowest  through  the  capillaries?  Why  in  the 
veins  quicker  than  in  the  capillaries,  but  slower  than  in  the  arteries? 

How  may  we  picture  the  vascular  system?  Illustrate.  How  do 
capillaries  differ  in  size  from  the  large  arteries? 

*  A  good  illustration  taken  from  physical  geography  is  afforded  by  the  Lake  of 
Geneva,  in  Switzerland.  This  is  supplied  at  one  end  by  a  river  which  derives  its 
water  from  the  melting  glaciers  of  some  of  the  Alps.  From  its  other  end  the 


22(5  THE  HUMAN  BODY. 

which,  though  thousands  of  times  smaller  than  the  great 
arteries  and  veins,  are  millions  of  times  more  numerous. 
The  channel  through  which  the  blood  flows  in  them  is, 
therefore,  when  they  are  all  taken  together,  very  much 
greater  than  that  to  which  it  is  confined  in  the  large  arterial 
and  venous  trunks. 

Why  there  is  no  Pulse  in  the  Capillaries  and  Veins. — 
The  heart  sends  blood  into  the  arteries  not  steadily  but 
intermittently;  each  beat  forces  in  some  blood,  and  then 
comes  a  pause  before  the  next  beat.  Accordingly  the  flow 
in  the  larger  arteries  is  not  even  and  continuous,  but  jerky, 
as  indicated  by  the  pulse. 

But  in  the  capillaries  the  flow  is  quite  steady,  and  yet  the 
capillaries  are  supplied  by  the  smaller  arteries.  We  have  to 
inquire  how  this  is  brought  about. 

The  disappearance  of  the  pulse  is  due  to  two  things,  (1) 
the  fact  that  in  the  tiny  capillaries  the  blood  meets  with 
considerable  resistance  to  its  flow,  dependent  on  friction, 
and  (2)  that  the  arteries  are  very  elastic. 

On  account  of  friction  in  the  capillaries  the  arteries  have 
difficulty  in  passing  on  blood  through  them;  blood  there- 
fore accumulates  in  the  aorta  and  its  large  branches  and 
stretches  their  elastic  walls.  The  stretched  arteries  press 
all  the  time  on  the  blood  inside  them,  and  constantly  keep 
squeezing  it  on  into  the  small  arteries  and  the  capillaries; 

How  in  number?  Is  the  total  blood  channel  greater  in  arteries  or 
capillaries?  In  veins  or  capillaries? 

Why  is  the  blood-flow  in  the  great  arteries  not  steady?  Name 
vessels  in  which  it  is  steady. 

To  what  is  the  loss  of  pulse  in  the  capillaries  due?  What  results 
from  friction  in  the  capillaries?  What  is  done  by  the  stretched 
arteries? 

water  is  carried  off  by  the  river  Rhone.  In  the  comparatively  narrow  inflowing 
and  outflowing  rivers  the  current  is  rapid ;  in  the  wide  bed  of  the  lake  it  is  much 
slower. 


ABSENCE  OF  PULSE  IN  THE  CAPILLARIES .    227 

both  while  the  heart  is  contracting  and  between  two  heart- 
beats. The  heart,  in  fact,  keeps  the  big  elastic  arteries 
over-distended  with  blood;  before  they  have  had  time  to 
nearly  empty,  another  systole  occurs  and  fills  them  up  tight 
again:  so  all  the  while  the  walls  of  the  arteries  are  stretched 

O  ? 

and  keep  pressing  on  ihe  blood  inside  them,  and  steadily 
forcing  it  on  into  the  capillaries.  The  heart  keeps  the 
arteries  over-full,  and  the  stretched  elastic  arteries  drive  the 
blood  through  the  capillaries.  As  the  arteries  are  always 
stretched  and  always  pressing  on  the  blood  the  capillaries 
receive  a  steady  supply,  and  the  flow  through  them  is  uni- 
form. This  even  capillary  flow  passes  on  a  steady  blood 
stream  to  the  veins.* 

The  object  of  having  no  pulse  in  the  capillaries  is  to 
diminish  the  danger  of  their  rupture.  As  we  have  seen, 
materials  from  the  blood  have  to  ooze  through  their  walls 
to  nourish  the  organs  of  the  body,  and  wastes  from  the 
organs  to  soak  back  into  the  blood  that  they  may  be  carried 
off.  Their  walls  have  therefore  to  be  very  thin;  and  if  the 

When?  "What  does  the  heart  do?  What  happens  before  the 
arteries  have  had  time  to  empty?  What  is  the  condition  of  the 
arterial  walls  all  through  life?  What  results  from  their  stretched 
condition?  What  keeps  the  arteries  tightly  filled?  What  sends 
blood  through  the  capillaries?  How  do  the  capillaries  get  a  steady 
blood  supply?  Why  do  we  find  a  uniform  current  in  the  veins? 

What  is  gained  by  having  no  pulse  in  the  capillaries?  What 
must  food  materials  in  the  blood  do  before  they  can  nourish  the 
body?  What  must  the  wastes  of  the  organs  do?  Why  must  the 
capillary  walls  be  very  thin? 

*  "  Every  inch  of  the  arterial  system  may,  in  fact,  be  considered  as  converting 
a  small  fraction  of  the  heart's  jerk  into  a  steady  pressure,  and  when  all  these 
fractions  are  summed  up  together  in  the  total  length  of  the  arterial  system  no 
trace  of  the  jerk  is  left.  As  the  effect  of  each  systole  becomes  diminished  in 
the  smaller  vessels  by  the  causes  above  mentioned,  that  of  this  constant  pres- 
sure becomes  more  obvious,  and  gives  rise  to  a  steady  passage  of  the  fluid  from 
the  arteries  towards  the  veins.  In  this  way,  in  fact,  the  arteries  perform  the 
same  functions  as  the  air-reservoir  of  a  fire-engine,  which  converts  the  jerk- 
ing impulse  given  by  the  pumps  .into  the  steady  flow  of  *he  delivery  hose."— 
HUXLEY. 


228  THE  HUMAN  BODY. 

blood  were  sent  into  them  in  sudden  jets  at  each  beat  of 
the  heart,  they  would  run  much  risk  of  being  torn. 

The  Muscles  of  the  Arteries. — The  arteries  have  rings  of 
plain  muscular  fibre  in  their  walls ;  when  these  contract 
they  narrow  the  artery,  and  when  they  relax  they  allow  it 
to  widen  under  the  pressure  of  the  blood  in  its  interior.  The 
vessel  then  carries  more  blood  to  the  capillaries  of  the  organ 
which  it  supplies.  Blushing  is  due  to  a  relaxation  of  the 
muscular  layer  of  the  arteries  of  the  face  and  neck,  allow- 
ing more  blood  to  flow  to  the  skin. 

Why  the  Arteries  have  Muscles. — The  amount  of  blood 
in  the  body  is  not  sufficient  to  allow  of  a  full  stream  of 
blood  through  all  its  organs  at  one  time:  the  muscular  fibres 
controlling  the  diameter  of  the  arteries  are  used  to  regulate 
the  blood-flow  in  such  a  manner  that  parts  hard  at  work 
shall  get  an  abundant  supply,  and  parts  at  rest  shall  only 
get  just  enough  to  keep  them  nourished.  Usually  when 
one  set  of  organs  is  at  work  and  its  arteries  dilated,  others 
are  at  rest  and  their  arteries  contracted.  Few  persons,  for 
example,  feel  inclined  to  do  brain-work  after  a  heavy  meal; 
for  then  a  great  part  of  the  blood  of  the  whole  body  is  led 
off  into  the  dilated  vessels  of  the  digestive  organs,  and  the 
brain  gets  but  a  small  supply.  On  the  other  hand,  when  the 
brain  is  at  work  its  vessels  are  dilated,  and  often  the  whole 
head  flushed;  and  when  the  muscles  are  exercised,  a  great 
portion  of  the  blood  of  the  body  is  carried  off  to  them ;  there- 

What  would  be  apt  to  happen  if  blood  were  sent  into  them  in 
sudden  jets? 

How  are  the  muscles  of  the  arteries  arranged?  What  results  from 
their  contraction?  From  their  relaxation?  To  what  is  blushing 
due? 

Why  cannot  all  the  organs  have  a  full  blood  stream  through  them 
at  the  same  time?  For  what  purpose  are  the  muscular  fibres  in  the 
walls  of  arteries  used?  What  is  the  usual  condition  of  the  arteries 
of  a  resting  organ? 


TAKING  COLD.  229 

fore,  hard  thought  or  violent  exercise  soon  after  a  meal  is  very 
apt  to  produce  an  attack  of  indigestion  by  diverting  the 
blood  from  the  abdominal  organs,  where  it  ought  to  be  at 
that  time.  Young  persons  whose  organs  have  a  super- 
abundance of  energy,  enabling  them  to  work  under  unfa- 
vorable conditions,  are  less  apt  to  suffer  in  such  ways  than 
their  elders.  One  sees  boys  running  actively  about  after 
eating,  when  older  people  feel  a  desire  to  sit  quiet  or  even 
to  go  to  sleep. 

Taking  Cold, — When  the  skin  is  chilled  its  arteries  con- 
tract, as  shown  by  the  pallor  of  the  surface.  This  throws 
an  undue  amount  of  blood  into  internal  parts,  whose  ves- 
sels become  gorged  with  blood  or  "congested,"  and  con- 
gestion very  easily  passes  into  inflammation.  Consequently, 
prolonged  exposure  of  the  surface  to  cold  is  very  apt  to  be 
followed  by  inflammation  of  parts  inside  the  body,  and 
give  rise  to  a  so-called  "cold"  (which  is  really  an  inflam- 
mation) of  the  mucous  membranes  of  the  head,  or  throat, 
or  lungs ;  or  of  the  intestines,  causing  diarrhoea.  In 
fact,  the  common  summer  diarrhoea  is  far  more  often 
due  to  a  chill  of  the  surface  leading  to  intestinal  inflam- 
mation than  to  the  fruits  eaten  in  that  season,  which 
are  so  often  blamed  for  it.  The  best  preventive  is  to 
wear  when  exposed  to  sudden  changes  of  temperature,  a 
woollen  or  at  least  a  cotton  garment  over  the  trunk  of  the 

Why  is  it  not  wise  to  take  hard  exercise  or  do  severe  mental  work 
soon  after  eating?  Why  do  young  persons  suffer  less  from  exercise 
soon  after  dinner  than  do  their  elders? 

What  happens  to  its  arteries  when  the  skin  is  chilled?  How  does 
this  manifest  itself?  What  is  its  result  on  the  blood-supply  of  in- 
ternal parts?  What  is  congestion?  Into  what  diseased  state  does  it 
often  pass? 

What  diseases  are  apt  to  follow  a  surface  chill?  What  is  the  most 
frequent  cause  of  summer  diarrho3a?  What  should  be  worn  when 
liable  to  exposure  to  considerable  changes  of  temperature? 


230  THE  HUMAN  BODY. 

body;  linen  permits  any  change  in  the  external  tempera- 
ture to  act  almost  at  once  upon  the  skin.  After  an  un- 
avoidable exposure  to  cold  or  wet,  the  thing  to  be  done  is 
of  course  to  maintain  the  cutaneous  circulation;  movement 
should  be  persisted  in,  and  a  thick  dry  outer  covering  put 
on  until  warm  and  dry  underclothing  can  be  obtained. 

In  healthy  persons,  a  temporary  exposure  to  cold,  as 
a  plunge  in  a  bath,  is  good,  since  in  them  the  sudden  con- 
traction of  the  cutaneous  arteries  soon  passes  off,  and  is 
succeeded  by  a  dilatation  causing  a  warm  healthy  glow  on 
the  surface.  If  the  bather  remain  too  long  in  cold  water, 
however,  this  reaction  passes  off,  and  is  succeeded  by  a  more 
persistent  chilliness  of  the  surface,  which  may  last  all  day. 
The  bath  should  therefore  be  left  before  this  occurs;  but 
no  absolute  time  can  be  stated,  as  the  reaction  is  more 
marked  and  lasts  longer  in  strong  persons  and  in  those  used 
to  cold  bathing  than  in  others. 

Why  does  linen  not  form  a  good  inner  garment  under  such  circum- 
stances? What  should  be  done  after  unavoidable  exposure  to  cold 
or  wet? 

Why  is  a  plunge  in  a  cold  bath  useful  to  healthy  persons?  What 
results  if  a  person  remains  too  long  in  cold  water?  When  should  a 
cold  bath  be  left?  What  persons  may  remain  longest  with  safety  in 
a  cold  baih? 


APPENDIX  TO  CHAPTER  XV. 

1.  A  frog  may  be  used  to  illustrate  the  beat  of  the  heart.     Ana- 
tomically a  frog's  heart  differs  in  many  respects  from  that  of  a  mam- 
mal, but  the  phenomena  of  systole  and  diastole  are  essentially  the  same. 

2.  Etherize  a  frog  as  before  described.     Cut  off  its  head.     Check 
bleeding  and  destroy  its  spinal  cord  by  forcing  a  pointed  wooden  peg 
along  the  spinal  canal. 

3.  Laying  the  animal  on  its  back,  carefully  divide  with  scissors 
the  skin  along  the  middle  line  of  the  ventral  surface  for  its  whole 
length.     Make  cross  cuts  at  each  end  of  this  longitudinal  one  and 
pin  out  the  flaps  of  skin. 


APPENDIX.  231 

4.  Next  pick  up  with  forceps  the  remaining  tissues  of  the  ventral 
near  its  posterior  end,  and  carefully  divide  them  longitudinally 

a  little  on  the  left  side  of  the  middle  line;  being  very  careful  not  to 
injure  either  the  viscera  in  the  cavity  beneath  or  a  large  vein  (ante- 
rior abdominal)  running  along  the  wall  in  the  middle  line. 

5.  About  the  point  where  you  see  this  vein  passing  from  the  wall 
to  enter  among  the  viscera  of  the  ventral  cavity,  youwill  come  to  the 
bony  and  cartilaginous  tissues  of  the  sternal  region.     Raise  the 
posterior  cartilage  in  your  forceps,  make  a  short  transverse  cut  in 
front  of  the  vein,  and,  looking  beneath  the  sternum,  note  the  peri- 
cardium with  the  heart  beating  inside  it.     Divide  the  fibrous  bands 
which  pass  from  the  pericardium  to  the  sternum,  and  with  scissors 
cut  away  sternum,  etc.,  taking  great  care  not  to  injure  the  heart. 

6.  Push  a  rod  about  half  an  inch  in  diameter  down  the  animal's 
throat  so  as  to  stretch  the  parts,  and  then  picking  up  the  pericardium 
in  a  pair  of  forceps,  open  it  and  gently  cut  it  away  from  about  the 
heart;  push  aside  any  lobes  of  the  liver  which  lie  on  the  latter  organ. 
In  the  heart  thus  exposed  note — 

a.  Its  beat;  a  regularly  alternating  contraction  (systole)  and  dila- 
tation (diastole). 

b.  In  consequence  of  the  destruction  of  the  spinal  cord  compara- 
tively little  blood  now  flows  through  the  heart,  but  during  the  con- 
traction you  will  be  able  to  observe  that  the  ventricular  portion, 
which  will  be  readily  recognized,  becomes  paler;  and  during  dias- 
tole again  becomes  deeply  colored,  getting  more  or  less  filled  up  with 
blood  which  shows  through  its  walls.  ' 

c.  Observe  that  each  contraction  starts  at  the  auricular  end  and 
travels  towards  the  ventricular;  this  may  be  more  easily  seen  by- 
and-by,  when  the  heart  begins  to  beat  more  slowly. 

7.  The  specimen  may  be  put  aside  under  a  bell-jar  with  a  wet 
sponge,  or  a  piece  of  flannel  soaked  in  water.     If  kept  from  drying 
the  heart  will  go  on  beating  for  hours. 

8.  To  demonstrate  the  action  of  the  valves  of  the  heart,  obtain  two 
uninjured  sheep's  hearts  from  a  butcher.     Remove  them  from  the 
pericardium,  taking  care  not  to  injure  the  vessels. 

9.  Cut  off  the  apex  of  one  heart  so  as  to  open  the  ventricles.     Then 
fill  up  the  stumps  of  the  aorta  and  the  pulmonary  artery  with  water. 
As  the  water  is  poured  in  the  semilunar  valves  will  be  seen  to  close 
up  and  block  the  passage  to  the  ventricle,  so  that  the  stump  of  the 
vessel  remains  full  for  some  time.     The  valves  rarely  act  quite  per- 
fectly in  a  heart  removed  from  the  body  and  treated  as  above,  but 
they  will  support  the  water  column  quite  long  enough  to  illustrate 
their  action. 


232          .  THE  HUMAN  BODY. 

10.  Carefully  cut  the  auricles  away  from  the  other  sheep's  heart, 
taking  great  care  not  to  injure  the  ventricles  or  the  auriculo-ventric- 
ular  valves.     Then  holding  the  ventricles,  apex  down,  in  one  hand, 
pour  water  in  a  stream  into  them  from  a  pitcher  held  about  a  foot 
above  them.     As  the  ventricles  fill, the  flaps  of  the  mitral  and  tricus- 
pid  valves  will  be  seen  to  float  up  and  cl®=ie  the  auriculo-ventricular 
orifice,  illustrating  their  movement  as  the  ventricle  fills  during  its 
diastole  in  the  natural  working  of  the  heart. 

11.  The  manner  in  which  the  elasticity  of  the  arteries  and  the  fric- 
tion resistance  to  flow  in  the  capillaries  together  serve  to  turn  a 
rhythmic  into  a  steady  flow  may  be  readily  demonstrated  as  follows: 

Take  an  elastic  bag  such  as  is  commonly  sold  with  enema  appara- 
tus in  drug-stores,  and  having  an  entry  and  exit  tube  provided  with 
valves  In  the  exit  tube  place  a  piece  of  glass  tubing  six  feet  long. 
Put  the  entry  tube  of  the  bag  in  a  basin  of  water.  On  pumping,  an 
intermittent  flow  of  water,  corresponding  to  the  strokes  of  the  pump, 
will  be  obtained  from  the  glass  tube.  Connect  a  very  fine  glass 
nozzle  with  the  end  of  the  long  tube;  on  pumping,  less  water  can 
be  forced  through,  and  the  outflow  is  still  rhythmic. 

12.  Replace  th2  glass  tube  by  a  rubber  tube  of  the  black,  highly 
elastic  kind  :  on  pumping  we  get  again  a  rhythmic  outflow.     Now 
connect  your  narrow  nozzle  to  the  end  of  the  rubber  tube,  and  pump : 
the  outflow  will  be  nearly  constant,  because  the  rubber  tube  not  being 
able  to  empty  itself  as  fast  as  the  water  is  pumped  into  it,  becomes 
stretched,  and  in  the  interval  between  two  strokes  of  the  pump  it 
keeps  on  squeezing  out  the  extra  water  accumulated   in  it.     The 
longer  and  more  elastic  the  tube,  the  quicker  and  stronger  the  stroke 
of  the  pump,  and  the  narrower  the  exit,  the  more  steady  will  be  the 
outflow.      In  the  body  the  heart  keeps  the  arteries  very  tightly 
stretched  all  the  time,  and  they  keep  up  accordingly  a  steady  flow 
into  the  capillaries.     The  experiment  shows  that  to  get  such  a  steady 
flow  two  things  are  necessary  :  (1)  that  the  tubes  fed  directly  by  the 
heart  shall  be  highly  elastic,  and  (2)  that  there  shall  be  considerable 
resistance  to  the  exit  from  their  outflow  ends 


CHAPTER  XVI. 
THE  OBJECT  AND  THE  MECHANICS  OF  RESPIRATION. 

The  Object  of  Respiration. — Blood  is  renewed,  so  far  as 
ordinary  food  materials  are  concerned,  by  substances  either 
directly  absorbed  by  the  blood-vessels  of  the  alimentary 
canal,  or  taken  up  by  the  lymphatics  of  the  digestive  tract 
and  afterwards  poured  into  the  blood.  But  in  order  that 
energy  may  be  set  free  for  use  by  the  tissues  of  the  body 
(Chap.  VIII. ),  oxidations  must  occur,  and  the  continuance 
of  these  vital  oxidations  depends  on  a  constant  supply  of 
oxygen.  As  their  result,  waste  substances  are  produced, 
which  are  no  longer  of  use  to  the  body,  but  detrimental  to 
it  if  present  in  large  quantity.  The  most  abundant  of 
these  wastes  is  carbon  dioxide  gas. 

The  function  of  respiration  has  for  its  objects  (1)  to 
renew  the  supply  of  oxygen  in  the  blood,  and  (2)  to  get  rid 
of  the  carbon  dioxide  produced  in  the  different  organs, 

The  Respiratory  Apparatus.— This  consists  primarily  of 
two  elastic  bags,  the  lungs,  placed  in  the  thorax,  filled  with 
air,  and  communicating  by  the  air-passages  with  the  sur- 

How  is  the,  blood  renewed  as  regards  ordinary  food  matters? 
What  must  occur  that  energy  be  set  free  for  use  by  the  body?  What 
is  necessary  that  the  oxidations  may  continue?  What  do  the  oxida- 
tions produce?  Which  is  the  most  abundant  waste  substance  of  the 
body? 

What  are  the  objects  of  respiration? 

Of  what  does  the  respiratory  apparatus  primarily  consist  ? 

[233] 


234  THE  HUMAN  BODY, 

rounding  atmosphere.  In  the  lungs  the  pulmonary  capil- 
lary blood-vessels  form  a  very  close  network:  through  their 
walls  the  blood  gives  off  to  the  air  in  the  lungs  carbon 
dioxide,  and  takes  from  this  air  oxygen.  The  air  in  the 
lungs  consequently  needs  renewal  from  time  to  time:  other- 
wise it  would  no  longer  have  oxygen  to  give  to  the  blood, 
iind  would  become  so  loaded  with  carbon  dioxide  as  to 
•40  longer  take  that  waste  product  from  it.  This  renewal 
is  effected  by  the  working  of  a  system  of  muscles,  bones, 
and  cartilages  whose  co-operation  brings  about  that  alter- 
nating expansion  and  contraction  of  the  chest  which  we  call 
breathing.  When  the  chest  contracts,  air  deprived  of  its 
oxygen  and  polluted  with  wastes  is  expelled  from  the  lungs; 
and  when  it  expands,  fresh  air,  rich  in  oxygen,  and  con- 
taining hardly  any  carbon  dioxide,  is  taken  into  them. 

The  respiratory  organs  are,  therefore,  (1)  the  lungs;  (2) 
the  air-passages;  (3)  the  vessels  of  the  pulmonary  circula- 
tion, including  the  pulmonary  artery  bringing  the  blood  to 
the  lungs,  the  pulmonary  capillaries  carrying  it  through 
them,  and  the  pulmonary  veins  conveying  it  from  them; 
(4)  the  muscles,  bones,  and  gristles  which  are  concerned  in 
producing  the  breathing  movements.* 

The  Air-Passages. — Air  reaches  the  pharynx  through 
the  nose  or  mouth  (Fig.  1) :  on  the  ventral  side  of  the  pharynx- 

What  vessels  form  a  close  network  in  the  lungs?  What  takes 
place  through  the  walls  of  these  vessels?  Why  must  the  air  in  the 
lungs  be  renewed?  How  is  the  renewal  brought  about?  What  is 
breathing?  What  happens  when  the  chest  contracts?  What  when 
it  expands  ? 

Enumerate  the  respiratory  organs. 

Through  what  passages  does  air  reach  the  pharynx? 

*  To  these  should  be  added  (5)  the  nerve  centres  and  nerves  which  control 
the  muscles  of  respiration,  and  which  will  be  subsequently  considered  (see 
Chap.  XX). 


THE  AIR-PASSAGES. 


235 


(Fig.  41)  is  an  aperture  through  which  it  passes  into  the 
larynx  or  voice-box  (a,  Fig.  64),  which  lies  in  the  upper 
part  of  the  neck.  From  the  larynx  air  passes  on  through 
the  windpipe  or  trachea;  this  enters  the  chest,  in  the  upper 


FIG.  64. 


FIG.  65. 


FIG.  64.— The  lungs  and  air-passages  seen  from  the  front.  On  the  left  of  the 
figure  the  pulmonary  tissue  has  been  dissected  away  to  show  the  ramifications 
of  the  bronchial  tubes,  a,  larynx  ;  6,  trachea;  d,  right  bronchus.  The  left  bron- 
chus is  seen  entering  the  root  of  its  lung. 

FIG.  65. — A  small  bronchial  tube,  a,  dividing  into  its  terminal  branches,  c,' 
thes •)  have  pouched  or  sacculated  walls  and  end  in  the  sacculated  alveoli.  6. 

* 

part  of  which  it  divides  into  a  right  and  a  left  bronchus. 
Each  bronchus  enters  a  lung,  and  divides  in  it  into  &  vast 
number  of  very  small  tubes,  called  the  bronchial  tubes. 
The  last  and  smallest  bronchial  tubes  (a,  Fig.  65)  open 
into  subdivided  elastic  sacs,  ~b,  c,  with  pouched  walls. 

What  aperture  is  found  on  the  ventral  side  of  the  pharynx? 
Where  does  the  larynx  He?  Where  does  the  air  go  from  the  larynx? 
Into  what  does  the  trachea  divide?  Where?  What  are  the  bronchial 
tubes?  How  do  the  final  bronchial  tubes  terminate? 


236  THE  HUMAN  BODY 

Structure   of  the  Windpipe   and  its  Branches.  —  The 

trachea,  bronchi,  and  bronchial  tubes  are  lined  by  mucous 
membrane,  outside  of  which  is  a  supporting  stratum  com- 
posed of  connective  and  plain  muscular  tissues.  Their  walls 
also  contain  cartilaginous  rings  or  half-rings  which  keep 
them  open.  Below  the  projection  on  the  throat  known  as 
Adam's  apple  (due  to  the  larynx,  see  Chap.  XXII.)  there 
may  readily  be  felt  in  thin  persons  the  stiff  windpipe  pass- 
ing down  to  the  top  of  the  chest. 

The  Cilia  of  the  Air-Passages. — The  mucous  membrane 
of  the  trachea  and  its  branches,  down  to  almost  the  smallest, 
has  a  layer  of  ciliated  cells  on  its  surface.  Each  of  these 
cells  has  on  its  end  turned  towards  the  cavity  of  the  tube  a 
tuft  of  from  twenty  to  thirty  slender  threads  which  are  in 
constant  motion;  they  lash  forcibly  towards  the  throat, 
move  gently  back  again,  and  then  once  more  violently  to- 
wards the  outlet  of  the  air-passage.  These  moving  threads 
are  called  cilia.  Swaying  in  the  mucus  secreted  by  the 
membrane  which  they  line,  they  sweep  it  on  to  the  throat, 
where  it  is  coughed  or  "hawked  "  up. 

Imagine  a  man  rowing  in  a  boat  at  anchor.  The 
sweep  of  the  oars  will  drive  the  water  back  and  not  the 
boat  forwards.  So  these  little  oars,  the  cilia,  being  an- 
chored on  the  mucous  membrane  drive  on  the  secretion 
which  bathes  its  surface. 


With  what  are  the  windpipe  and  its  branches  lined?  What  lies 
outside  this  lining?  What  do  these  walls  also  contain?  What  is 
the  use  of  the  cartilages?  What  is  "  Adam's  apple"?  What  may  be 
felt  below  it  in  front  of  the  neck? 

What  lines  the  mucous  membrane  of  the  windpipe  and  its  sub- 
divisions? What  does  each  ciliated  cell  bear  on  its  free  end?  How 
do  the  threads  move?  What  are  they  called?  What  is  the  use  of 
the  cilia  of  the  air-passages? 

Illustrate  how  they  push  on  the  liquid  they  move  in, 


THE  LUNG 8. 


237 


Bronchitis,  or  "a  cold  on  the  chest,"  is  an  inflamma- 
tion of  the  membrane  lining  the  bronchial  tubes,  in  con- 
sequence of  which  it  swells,  and  secretes  an  extra  amount 
of  mucus.  The  swelling  and  secretion  tend  to  close  the 
tabes  and  interfere  with  the  free  passage  of  air  in  breathing. 

The  Lungs  consist  of  the  bronchial  tabes  and  their  ter- 
minal dilatations,  together  with  blood-vessels,  lymphatics, 
and  nerves,  all  bound  firmly  together  by  elastic  tissue. 
The  expansions  called  "  air-cells"  *  at  the  end  of  each  final 
branch  of  a  bronchial  tube  (Fig. 
66)  are  relatively  very  large, 
and  their  surface  is  still  fur- 
ther increased  by  the  pouches 
(«,  V)  which  project  from  them. 
Their  walls  are  highly  elastic, 
and  contain  a  close  network  of 
capillary  blood-vessels,  supplied 
by  the  pulmonary  artery  and 
emptying  into  the  pulmonary 
veins.  Through  the  extremely 
thin  lining  of  the  air-cell,  and 

.,        .  ,  .  *ii      £  ii  -n      •  FlG-  66.—  Two  alveoli  of  the  lung 

the   thin  Wall  OI  the   Capillaries  highly  magnified.     6,  6,  the  air-cells, 
.  .  ,      or  hollow  protrusions  of  the  alveo- 

imbedded.   Ill    It,  OXygen    IS    au-  lus,  opening  into  its  central  cavity; 

c,  terminal   branches  of   bronchial 

sorbed  by  the  blood  from  the  tube. 


air  in  the  air-cell  and  carbon  dioxide  given  up  to 


It 


"What  is  bronchitis?  How  does  an  attack  of  bronchitis  interfere 
with  breathing? 

Of  what  do  the  lungs  consist?  What  are  the  air-cells?  How  is 
their  surface  increased?  What  do  their  walls  contain?  By  what  are 
their  capillaries  filled,  and  into  what  do  they  empty?  What  inter- 
change between  blood  and  air  occurs  in  the  air-cells  of  the  lungs? 

*  Cell  is  here  used  in  its  primitive  sense  of  a  small  chamber  or  cavity  (Latin, 
cellula),  and  not  in  its  modern  histological  signification,  as  one  of  the  distinct 
pieces  of  living  matter  recognized  by  the  microscope  as  serving  to  build  up  the 
body  by  their  accumulation  and  co  operation. 


238  THE  HUMAN  BODY. 

has  been  calculated  that  if  the  walls  of  the  air-cells  were 
all  spread  out  flat  and  placed  side  by  side  they  would  cover 
an  area  of  2600  square  feet.  This  great  surface,  therefore, 
represents  the  area  of  the  body  by  which  oxygen  is  received 
and  carbon  dioxide  given  off. 

The  Pleura. — The  exterior  of  each  lung,  except  where 
its  bronchus  and  blood-vessels  enter  it,  is  covered  by  a 
thin  elastic  serous  membrane,  the  pleura  (Fig.  2).  This 
membrane  also  lines  the  inside  of  the  chest.  Its  surface  in 
health  is  kept  moistened  by  a  small  quantity  of  lymph. 
In  consequence  of  its  smoothness  and  moisture,  during  the 
breathing  movements  the  chest  wall  and  lung  glide  over 
each  other  with  hardly  any  friction. 

Pleurisy  is  inflammation  of  the  pleura.  In  its  early 
stages  it  is  usually  associated  with  sharp  pain  on  drawing  the 
breath.  Later  on  a  large  quantity  of  lymph  is  often  poured 
out  by  the  inflamed  pleura,  filling  up  the  cavity  which 
should  be  occupied  by  the  lung,  and  pressing  the  latter  up 
into  a  small  mass,  very  inefficient  for  breathing  purposes. 

The  Elasticity  of  the  Lungs. — The  lungs  are  so  elastic  as 
to  be  like  a  thin  india-rubber  bag.  If  we  tie  a  tube  tightly 
into  a  bronchus  and  blow  in  air  the  lung  will  dilate,  but  as 
soon  as  we  cease  blowing  and  leave  the  tube  open,  it  will 
shrink  up  again.  Yet  in  the  chest  the  lungs  always  remain 
so  expanded  as  to  completely  fill  up  all  the  space  left  for 
them  by  the  heart  and  other  things  contained  in  the 
thorax.  How  is  this  ? 

How  large  is  the  surface  of  the  body  set  apart  for  oxygen  recep- 
tion and  carbon  dioxide  elimination? 

What  is  the  pleura?  What  does  it  cover  besides  the  outer  surface 
of  each  lung?  What  is  its  condition  in  health?  What  is  its  use? 

What  is  pleurisy?  What  symptom  usually  accompanies  its  early 
stages?  What  happens  later? 

What  do  the  lungs  resemble  in  their  elasticity?  How  ma}T  this 
elasticity  be  demonstrated?  What  is  the  natural  condition  of  the 
Kings  in  the  Ghent? 


EXPANSION  OF  THE  L  UNGjS.  239 

Why  the  Lungs  remain  expanded. — We  may  best  under- 
stand this  by  considering  a  thin  india-rubber  bag,  such  as  a 
toy  balloon.  If  the  neck  of  the  bag  is  open  it  collapses. 
Why  ?  Because  the  atmosphere,  which  pushes  on  all 
things  near  the  earth's  surface  with  a  pressure  of  about 
15  Ibs.  on  each  square  inch  (1033  grams  on  each  square  cen- 
timetre), presses  equally  on  the  outside  and  the  inside  of 
the  bag.  These  pressures  balance  one  another,  and  the  bag 
collapses  on  account  of  its  elastic  contractility. 

We  can  expand  such  a  bag  in  two  ways.  We  may  blow 
air  into  it  forcibly,  and  so  make  the  pressure  inside  suffi- 
ciently greater  than  the  opposing  aerial  pressure  outside  to 
overcome  the  elasticity  of  the  bag.  But  we  can  also  dis' 
tend  the  bag,  not  by  increasing  the  aerial  pressure  inside  it, 
but  by  diminishing  that  outside  it. 

Suppose  (Fig.  67)  we  tie  our  rubber  bag  (d)  on  the  lower 
end  of  the  tube  £,  which,  like  the  tube  c,  passes 
air-tight  through  a  cork,  and  then  fit  the  cork 
tightly  into  the  glass  bottle  A.  The  air  will 
then  press  with  its  full  weight  on  the  inside  of 
the  bag  through  1)  and  on  the  outside  of  it 
through  c,  and  the  bag  will  remain  collapsed. 
If  now  we  suck  air  out  through  c  we  diminish 
its  pressure  on  the  outside  of  the  bag  without  FlG-  *?•—: Di^- 

*  gram   mustrat- 

altering  the  atmospheric  pressure  on  its  inside:  refa^shlpTof 
tf  will  therefore  begin  to  expand,  because  the  Soraxgs  in  the 
pressure  inside  it  is  no  longer  counterbalanced  by  the  pres- 
sure outside.  The  more  air  we  suck  out  of  c  (that  is,  the  more 
we  diminish  the  atmospheric  pressure  on  the  exterior  of  d) 


Why  does  a  thin  rubber  bag  collapse  when  its  neck  is  open? 

How  can  we  expand  such  an  elastic  bag?  Describe  a  model  illus- 
trating the  means  by  which  the  lungs  are  kept  expanded  in  the  chest- 
and  explain  its  action? 


240  THE  HUMAN  BODY. 

the  more  will  the  bag  expand.  Finally,  if  the  rubber  bag 
is  distensible  enough,  when  all  the  air  in  the  bottle  is 
sucked  out  d  will  be  distended  by  the  push  of  the  air  inside 
it  until  it  completely  fills  the  bottle,  whose  walls  prevent 
it  from  going  any  farther.  If  now  we  open  c  and  let  in 
the  outside  air,  the  bag  will  again  collapse  to  its  original 
shrunken  dimensions. 

Application  to  the  Lungs. — The  above  experiment  illus- 
trates very  perfectly  how  the  lungs  are  kept  distended  dur- 
ing life.  The  chest  is  an  air-tight  chamber  containing, 
among  other  things,  the  elastic  hollow  lungs.  On  the 
interior  of  the  lungs  the  weight  of  the  atmosphere  presses 
through  the  air-passages  which  lead  to  them,  and  answer 
to  the  tube  b  in  Fig.  67.  Outside  the  lungs  in  the  thorax 
there  is  no  air  at  all,  and  the  uncounterpoised  aerial  pres- 
sure inside  them  overcomes  their  tendency  to  shrink,  and 
expands  them  so  as  to  completely  fill  all  holes  and  corners 
of  the  thoracic  chamber  not  occupied  by  other  organs.  If, 
however,  we  make  a  hole  in  the  chest  wall  and  let  the  air 
press  on  the  outside  of  the  lungs  they  collapse  at  once. 

How  the  Air  is  renewe.d  in  the  Lungs. — Suppose  in  Fig. 
S7  that  the  bottle  A  has  a  movable  bottom,  by  pulling  down 
rtrhich  its  capacity  can  be  increased,  and  that  all  air  has 
been  sucked  out  of  the  bottle  through  c,  which  is  then 
closed.  The  elastic  bag  will  then  be  distended  by  the  weight 
of  the  atmosphere  acting  upon  its  interior  so  as  to  fill  the 
bottle  and  press  against  its  sides.  If  now  the  movable 
bottom  of  A  be  pulled  down  so  as  to  make  the  cavity  of  the 

Apply  to  the  lungs  the  facts  illustrated  by  the  model  represented 
in  figure  67. 

Suppose  we  have  a  bottle  like  that  in  Fig.  67,  but  with  a  movable 
bottom,  what  would  happen  when  the  bottom  was  pulled  down  < 


RENEWAL    OF   AIR    IN   LUNGS. 


241 


bottle  larger,  the  bag  would  have  a  larger  space  to  fill. 
The  impediment  on  its  outside  being  removed  the 
atmospheric  pressure  on  its  inside  would  expand  it 
still  further,  and  the  elastic  bag  would  swell  out  to 
fill  the  extra  space.  As  the  movable  bottom  was  pulled 
down,  the  bag  would  enlarge  and  receive  fresh  air 


FIG.  08.— The  skeleton  of  the  thorax,    a,  g,  vertebral  column;  &,  first  rib;  c, 
clavicle ;  d,  third  rib ;  i,  glenoid  fossa. 

through  #.  When  the  bottom  was  raised  again  the  bag 
would  diminish,  and  some  air  be  driven  out  of  it  through  b. 
It  is  in  quite  a  similar  way  that  the  air  is  renewed  in  our 
lungs  by  breathing.  When  we  breathe-in,  the  thoracic 
cavity  is  enlarged  and  air  enters  the  lungs;  when  we 

How  would  the  bag  inside  it  be  affected? 

What  would  the  bag  receive?    What  would  happen  when  the 
bottom  was  again  raised?     What  happens  when  we  breathe-in? 


242  THE  HUMAN  BODY. 

breathe-out,  the  thorax  is  diminished  and  air  driven  out 
of  the  lungs. 

Inspiration  and  Expiration. — The  process  of  taking  air 
into  the  lungs  is  known  as  inspiration,  that  of  expelling  it 
as  expiration.  On  the  average,  fifteen  to  eighteen  inspira- 
tions and  expirations  occur  in  each  minute.  We  therefore 
breathe  in  and  out  about  once  for  every  four  beats  of  the 
heart. 

The  Structure  of  the  Thorax. — The  thorax  is  a  conical 
cavity  with  a  rigid  supporting  skeleton  (Fig.  68)  formed  by 
the  dorsal  vertebrae  behind,  the  breast  bone  in  front,  and 
the  ribs  and  rib  cartilages  on  the  sides.  Between  and  over 
these  lie  muscles,  and  the  whole  is  covered  air-tight  by  the 
skin  outside  and  the  pleura  (p.  238)  inside.  Above,  it  is 
closed  by  the  muscles  and  other  organs  of  the  neck;  and 
below  by  a  movable  bottom,  the  diaphragm.  The  air-tight 
chamber  thus  bounded  can  be  enlarged  in  all  three  diame- 
ters, but  especially  in  the  vertical,  and  in  that  running 
from  the  spinal  column  to  the  breastbone  (dorso-ventral 
diameter). 

The  Vertical  Enlargement  of  the  Thorax.  —  This  is 
brought  about  by  the  contraction  of  the  diaphragm,  which 
(as  may  be  seen  in  Fig.  69),  is  a  thin  sheet  of  muscle,  with 
a  fibrous  membrane  in  its  centre  serving  as  a  tendon.  In  rest 
the  diaphragm  is  dome-shaped,  its  concavity  being  turned 
towards  the  abdomen.  From  the  tendon  on  the  crown  of 

What  when  we  breathe-out? 

What  is  inspiration?  Expiration?  How  often  does  each  occur  in 
a  minute?  Compare  the  rate  of  respiration  and  of  the  heart-beat? 

What  is  the  form  of  the  thorax?  What  forms  its  skeleton?  What 
lie  between  and  over  its  bones  and  cartilage?  How  is  it  closed  air- 
tight? 

How  is  the  chest  closed  above?  How  below?  In  what  diameters 
can  the  chest  cavity  be  enlarged? 

Describe  the  diaphragm. 


THE  DIAPHRAGM.  243 

the  dome,  striped  muscular  fibres  radiate,  downwards  and 
outwards,  in  all  directions,  and  are  fixed  by  their  inferior 
ends  to  the  lower  ribs,  the  breast-bone,  and  the  vertebral 
column.  In  inspiration  (drawing  a  breath)  the  muscular 


FIG.  69.— The  lower  half  of  the  thorax,  with  four  lumbar  vertebrae,  showing 
the  diaphragm  from  above.      1,  2,'  3,  central  tendon;  4,  5,  muscular  part. 


fibres,  shortening,  flatten  the  dome  and  so  enlarge  the 
thoracic  cavity  at  the  expense  of  the  abdominal.  The  con- 
traction of  the  diaphragm  thus  greatly  increases  the  size  of 
the  thorax  chamber  by  adding  to  its  lowest  and  widest 
part. 

What  happens  to  it  during  inspiration?    What  results? 


244  THE  HUMAN  BODY. 

The  Dorso-Ventral  Enlargement  of  the  Thorax.— The  ribs 
on  the  whole  slope  downwards  (Fig.  15)  from  the  vertebral 
column  to  the  breast-bone,  the  slope  being  most  marked  in 
the  lower  ones.     During  inspiration 
the  breast- bone  and  the  sternal  ends 
of  the  ribs  attached  to  it  are  raised 
by  muscles  which  pull  on  them,  and 
so  the  distance  between  the  sternum 
and    the    vertebral    column    is  in- 
creased.    That  this  must  be  so  will 
readily  be  seen  by  examining    the 
diagram  Fig  70,  where  ab  represents 
FIG.  70.  — Diagram  iiius-  the  vertebral   colunjn,  c  and  d  two 

trating  the  dorso -ventral  in-       .,  ..  .  , 

crease  in  the  diameter  of  the  ribs,  and  st  the  sternum.  The 
thorax  when  the  ribs  are 

raised.  continuous  lines  represent  the  natu- 

ral position  of  the  ribs  at  rest  in  expiration,  and  the 
dotted  lines  the  position  in  inspiration.  It  is  clear 
that  when  their  lower  ends  are  raised  so  as  to  make 
the  bars  lie  in  a  more  horizontal  plane,  the  sternum  is 
pushed  away  from  the  spine,  and  so  the  extent  of  the 
chest  cavity  between  back-bone  and  breast-bone  is  in- 
creased. 

Expiration. — Inspiration  requires  a  good  deal  of  muscu- 
lar effort.  When  the  diaphragm  contracts  and  flattens  its 
dome  it  has  to  push  down  the  abdominal  viscera  on  its 
under  side,  and  to  press  out  the  front  wall  of  the  abdomen 
to  make  room  for  them.  The  ribs  and  breast-bone  have 
also  to  be  pulled  up  out  of  their  natural  position  of  equilib^ 


What  is  the  general  direction  of  the  ribs?  How  is  it  altered! 
during  inspiration?  What  is  the  consequence?  Illustrate  by  refer 
ence  to  a  diagram. 

Why  does  inspiration  require  muscular  effort? 


EXPIRATION.  245 

rium.      In  ordinary  expiration,  on  the  contrary,  but  little 
if  any  muscular  effort  is  required. 

As  soon  as  the  muscles  which  have  raised  the  ribs  and 
sternum  relax,  these  bones  return  to  their  natural  uncon- 
strained position;  and  the  elastic  abdominal  wall  presses 
the  abdominal  viscera  against  the  under  side  of  the  dia- 
phragm and  pushes  that  organ  up  again,  as  soon  as  its 
muscular  fibres  cease  contracting.  In  this  way  the  chest 
cavity  is  restored  to  its  original  capacity,  and  the  air  is 
sent  out  of  the  lungs  rather  by  the  elasticity  of  the  parts 
which  were  stretched  in  inspiration,  than  by  any  special 
expiratory  muscles. 

When,  however,  an  expiration  is  violent  (when,  for  ex- 
ample, we  try  to  empty  our  lungs  of  air  as  completely  as 
possible,  or  during  a  fit  of  coughing)  special  expiratory 
muscles,  which  pull  down  the  ribs  and  press  up  the  dia- 
phragm, are  called  into  action. 

The  Respiratory  Sounds. — The  entry  and  exit  of  air  are 
accompanied  by  the  respiratory  sounds  or  murmurs,  which 
can  be  heard  on  applying  the  ear  to  the  chest  wall.  The 
character  of  these  sounds  is  different  and  characteristic 
over  the  trachea,  the  larger  bronchial  tubes,  and  portions 
of  lung  from  which  large  bronchial  tubes  are  absent.  They 
are  variously  modified  in  pulmonary  affections,  and  hence 
the  value  of  auscultation  of  the  lungs  in  assisting  the  phy- 
sician to  form  a  diagnosis. 

Hygienic  Remarks. — Since  the  diaphragm  when  it  con- 
How  does  expiration  differ  from  it  in  this  respect? 
Explain  how  the  chest  is  brought  hack  to  its  resting  position  after 
an  inspiration? 

Give  examples  of  violent  expiration?  How  does  it  differ  from 
an  ordinary  expiration  in  the  forces  at  work  for  its  production? 

What  are  the  respiratory  sounds?  Where  do  their  characters 
differ?  Why  do  physicians  study  them  in  lung  diseases? 


246 


THE  HUMAN  BODY. 


tracts  pushes  down  the  abdominal  viscera  lying  against  its 
under  side,  these  have  to  make  room  for  themselves  by 
pushing  out  the  soft  front  of  the  abdomen,  which  accord- 
ingly protrudes  when  the  diaphragm  descends.  Hence 
breathing  by  the  diaphragm  is  indicated  on  the  exterior  by 


FIG.  71. 

FIG.  71.— Torso  of  the  Statue 
known  as  Venus  of  Milo. 


FIG.  73. 

FIG.  72.— Paris  Fashion,  May, 
1880. 


movements  of  the  abdomen,  and  is  often  called  ' '  abdominal 
respiration,"  as  distinguished  from  breathing  by  the  ribs, 
called  "costal"  or  "chest  breathing."  In  both  sexes  the 
diaphragmatic  breathing  is  the  more  important,  but,  as  a 
rule,  men  and  children  use  the  ribs  less  than  adult  women. 

Why  does  the  abdomen  protrude  during  an  inspiration?  What  is 
meant  by  abdominal  respiration?  Why?  What  is  costal  respira 
tion?  Which  form  of  breathing  is  most  developed  in  women? 


APPENDIX.  247 

Since  abdomen  and  chest  alternately  expand  and  contract 
in  healthy  breathing,  anything  which  impedes  their  free 
movement  is  to  be  avoided:  the  tight  lacing  which  used  to 
be  thought  elegant,  and,  indeed,  is  still  indulged  in  by 
some  who  think  a  distorted  form  beautiful,  seriously  im- 
pedes one  of  the  most  important  functions  of  the  body, 
leading  not  only  to  shortness  of  breath  and  an  incapacity  for 
muscular  exertion,  but,  as  has  been  proved,  in  many  cases 
to  actual  disease.  In  extreme  cases  of  tight  lacing  some 
organs  are  often  directly  injured,  weals  of  fibrous  tissue 
being,  for  example,  not  unfrequently  found  developed  on 
the  liver  from  the  constant  pressure  of  the  lower  ribs  forced 
against  it  by  a  tight  corset. 

Why  should  conditions  impeding  the  movement  of  chest  and 
abdomen  be  avoided?  What  is  the  result  of  tight  lacing?  What  is 
of  tea  found  on  examining  after  death  the  bodies  of  persons  who 
have  practised  tight  lacing  for  a  long  time  ? 


APPENDIX  TO   CHAPTER  XVI. 

1.  A  sheep's  lungs  with  the  windpipe  attached  may  be  readily  ob- 
tained from  a  butcher.     It  is  best  to  secure  it  and  the  heart  all  in  one 
mass,  as  unless  the  heart  be  carefully  removed  holes  are  apt  to  be 
cut  in  the  lung. 

2.  Examine  the  windpipe,  and  trace  it  down  to  its  division  into  the 
bronchi.     In   the  wall  of  the  windpipe  note  the  horse-shoe-shaped 
cartilages  which  keep  it  open,  and  which  are  so  arranged  that  the 
dorsal  aspect  of  the  tube  (which  lies  against  the  gullet)  has  no  hard 
parts  in  it. 

3.  Trace  one  bronchus  to  its  lung,  and  then  cutting  away  the  lung 
tissues  follow   the   branching  bronchial  tubes   through  the   organ. 
Note  the  cartilages  in  their  walls. 

4.  Carefully  divide  the  other  bronchus  where  it  joins  the  wind- 
pipe, and  lay  it  and  its  lung  aside.     Then  slit  open  the  trachea,  the 
bronchus  still  attached  to  it  and  the  bronchial  tubes.     Observe  the 
soft  pale-red  mucous  membrane  lining  them. 


248  THE  HUMAN  BODY. 

5.  In  the  bronchus  which  has  still  an  uninjured  lung  attached  to 
it  tie  air-tight  a  few  inches  of  glass  or  other  tubing  of  convenient  size. 
On  the  end  of  the  glass  tube  then  slip  a  few  inches  of  rubber  tubing. 
On  blowing  through  the  rubber  tube  the  lung  will  be  distended,  and 
as  soon  as  the  opening  is  left  free  it  will  collapse;  in  this  way  its 
great  extensibility  and  elasticity  will  be  seen. 

6.  Blow  up  the  lung  moderately,  and  while  it  is  distended  tie  a 
string  very  tightly  around  the  bit  of  rubber  tubing.     This  will  keep 
the  air  from  escaping;  the  distended  lung  can  now  be  examined  at 
leisure,  and  its  form,  lobes,  and  the  smooth  moist  pleura  covering  it 
be  better  seen  than  when  it  is  collapsed. 

7.  To  construct  the  very  instructive  model   depicted   in  Fig.  67, 
obtain  a  wide-necked  glass  vessel,  and  a  rubber  toy  balloon.     Very 
carefully  untie  and  open  the  neck   of  the  balloon,  and  tie   into  it 
tightly  a  glass  rod.     Take  a  cork  (one  of  rubber  is  best)  which  fits 
the  neck  of  the  bottle  tightly  and  is  perforated  by  two  holes;  through 
one  of  these  holes  pass  the  tube  projecting  from  the  neck  of  the 
balloon  in  such  way  that  the  collapsed  balloon  is  on  the  under  side 
of  the  cork.     Through  the  other  hole  pass,  air-tight,  a  tube  bent  as 
shown  in  the  figure,  and  on  the  upper  end  of  tbis  slip  a  few  inches 
of  rubber  tubing.    (Tins  can  be  pinched  or  tied  up  at  any  time,  and  in 
that  way  closed,  and  so  forms  a  cheap  substitute  for  the  stopcock 
represented  in  the  figure).     When  the  cork  is  now  secured   firmly 
in  the  bottle  the  apparatus  is  ready  for  use  as  indicated  on  p.  239. 

8.  Substitute  a  lung  for  the  rubber  balloon  in  the  above  experi- 
ment. 

9.  The  action  of  the  diaphragm  may  be  illustrated  by  substituting 
for  the  bottle  of  §  7  a  bell-jar  with  a  wide  neck  at  its  upper  end. 
Take  a  piece  of  sheet  rubber  somewhat  larger  than  the  bottom  of  the 
bell-jar,  and  tie  a  button  or  marble  in  the  centre  of  it.     Lay  the  rub- 
ber on  the  table,  with  the  projection  caused  by  the  button  down- 
wards.    On  it  place  the  bell  jar,  stretch  the  rubber  moderately  tight, 
turn  its  edges  up  around  the  margin  of  the  bell-jar,  and  tie  very 
tightly  with  waxed  cord  or  copper  wire.     In  the  neck  of  the  bell- 
jar  place  a  tight  cork  with  tubes  and  rubber  balloon,  as  described  in 
§  7.     Suck  air  out  of  the  bottle  until  the  balloon  is  fairly  well  ex- 
panded; then  tie  the  rubber  tube.     As  the  air  is  removed  the  pressure 
of  the  atmosphere  on  its  exterior  will  cause  the  rubber  sheet  to  arch 
up  into  the  cavity  of  the  bell- jar  so  that  it  now  fairly  well  represents 
the  diaphragm.     The  knob  caused  by  the  button  serves  as  a  handle 
by  which  this  artificial  diaphragm  may  be  pulled  down,  representing 
inspiration;  as  it  descends  the  balloon  (lung)  enlarges,  and  air  enters 
it  from  outside.     When  the  button  is  let  go  the  artificial  diaphragm 


APPENDIX.  249 

ascends,  the  lung  collapses,  and  air  is  forced  out  of  it  (expiration). 
Then  open  the  air  tube  leading  into  the  bell-jar.  The  lung  will  col- 
lapse, and  the  movements  of  the  diaphragm  have  no  influence 
upon  it. 

10.  The  diaphragm  itself  may  be  readily  seen  on  the  body  of  any 
small  animal  (rat,  kitten,  puppy),  on  removing  the  abdominal  vis- 
cera. The  liver  and  stomach  must  be  cut  away  with  especial  care. 

a.  When  the  above  viscera  are  removed  the  vaulted  diaphragm 
will  be  seen,  and  through  it  the  pink  lungs. 

b.  Seizing  some  of  the  folds  of  peritoneum  attached  to  the  dia- 
phragm, pull  it  down,  imitating  its  contraction  and  flattening  in  in- 
spiration.    The  lungs  will  be  seen  to  follow  it  closely,  expanding  to 
fill  the  space  left  by  it  in  its  descent. 

c.  Make  a  free  opening  into  one  side  of  the  thorax.     The  corre- 
sponding lung  will   collapse,  and  be  no  longer   influenced  by  move- 
ments of  the  diaphragm. 

d.  Now  open  the  other  side  of  the  chest:  its  lung  also  shrinks  up; 
the  structure  of  the  diaphragm  (its  tendinous  centre  and  muscular 
peripheral  regions)  can  now  be  better  seen,  as  also  the  attachment  of 
the  pericardium  to  its  thoracic  side. 

11.  The  action  of  the  microscopic  cilia  in  driving  along  the  mucus 
in  which  they  move  may  be  demonstrated  as  follows: 

a.  Cut  off  a  frog's  head  and  destroy  its   spinal   cord   (p.  230) 
Then  cut  out  its  gullet  as  completely  as  possible;  slit  this  open  and 
spread  it  out,  inner  side  up,  on  a  piece  of  cork  or  board,  and  fix  it 
with  pins  stuck  through  its  edges. 

b.  Prepare  a  very  thin  and  small  shaving  of  cork.     Dissect  the 
skin  off  one  thigh  of  the  animal  and  wrap  a  bit  of  it  round  the  shav- 
ing of  cork,  with  its  underside  outwards. 

c.  Place  the  light  mass  thus  formed  on  the  mucous  membrane  of 
the  gullet,  near  its  mouth  end.    The  little  mass  will  slowly  be  moved 
along  to  the  stomach  end  of  the  gullet,  and  if  returned  to  the  mouth 
end  time  after  time  will  be  swept  along  in  the  same  direction.     This 
is  due  to  the  cilia  which  line  the  frog's  gullet  (they  are  not  present 
In  that  of  man),  and  push  along  to  the  stomach  the  mucus  bathing 
them  on  which  the  little  float  swims. 

d.  Place  the  exposed  gullet  under  a  bell- jar  with  a  wet  sponge  for 
an  hour  or  two.     The  mucus  secreted  by  it  will  be  found  to  have 
been  swept  along  to  the  end  of  it  which  joins  the  stomach. 


CHAPTER    XVII. 

THE  CHEMISTRY  OF  RESPIRATION  AND  VENTILATION. 

The  Quantity  of  Air  breathed  daily. — After  an  ordi- 
nary expiration  the  chest  cavity  is  by  no  means  completely 
collapsed.  At  this  time  the  lungs  still  contain  about  200 
cubic  inches  of  air.  In  the  next  inspiration  30  more  cubic 
inches  are  taken  in,  about  the  same  amount  sent  out  at  the 
following  expiration,  and  so  on  throughout  the  day.  Du- 
ring quiet  breathing  the  quantity  of  air  in  the  lungs  varies, 
therefore,  with  each  inspiration  and  expiration  between  230 
and  200  cubic  inches.  At  each  inspiration  something  over 
a  pint  of  fresh  air  is  taken  in,  and  at  each  expiration  about 
the  same  amount  of  vitiated  air  is  expelled.  As  each  of 
us  breathes  at  least  fifteen  times  a  minute,  we  thus  use  each 
minute,  and  render  impure,  15x30— 450  cubic  inches  (15| 
pints)  of  air.  In  an  hour  the  quantity  would  be  450  X  60 
=  27,000  cubic  inches  (930  pints),  and  in  twenty-four 
hours  27,000X24=648,000  cubic  inches  (22,320  pints)  of 
air,  which  would  weigh  about  28. 7  Ibs.  We  have  next  to 

How  much  air  do  the  lungs  contain  after  an  ordinary  expiration? 
How  much  do  they  receive  at  the  next  inspiration?  How  much  is 
sent  out  from  them  during  expiration?  Within  what  limits  does  the 
quantity  of  air  in  the  lungs  vary  during  quiet  breathing?  What  bulk 
of  air  is  taken  in  during  an  inspiration? 

How  often  do  we  breathe?  How  much  air  does  each  one  of  us 
render  impure  every  minute?  How  much  in  an  hour?  How  many 
pints  in  a  day?  What  does  this  quantity  of  air  weigh? 

[250] 


CHANGES  IN  RESPIEED  AIR.  251 

see  what  it  is  that  happens  to  this  vast  quantity  of  air 
breathed  daily  by  each  one  of  us;  what  we  have  taken  out 
of  it,  and  what  we  have  given  off  to  it. 

The  Changes  produced  in  Air  by  being  once  breathed. — • 
These  are  fourfold — changes  in  its  temperature,  in  its  mois- 
ture, in  its  chemical  composition,  and  in  its  volume. 

Temperature  Changes. — The  air  taken  into  the  lungs  is 
nearly  always  cooler  than  that  expired,  which  has  a  tem- 
perature of  about  36°  C.  (97°  F.).  The  temperature  of  a 
room  is  usually  about  21°  C.  (70°  F.).  The  warmer  the 
inspired  air,  the  less  the  heat  which  is  lost  to  the  body  in 
the  breathing  process. 

Changes  in  Moisture. — Inspired  air  always  contains  more 
or  less  water  vapor,  but  is  rarely  saturated — that  is,  rarely 
contains  so  much  but  it  can  take  up  more  without  showing 
it  as  mist;  the  warmer  air  is,  the  more  water  vapor  it  re- 
quires to  saturate  it.  The  expired  air  is  nearly  saturated 
for  the  temperature  at  which  it  leaves  the  body,  as  is  read- 
ily shown  by  the  vapor  deposited  when  it  is  slightly  cooled, 
as  when  a  mirror  is  breathed  upon;  or  by  the  clouds  seen 
issuing  from  the  nostrils  on  a  frosty  day,  these  being  due 
to  the  fact  that  the  air  as  soon  as  it  is  cooled  cannot  hold 
all  the  water  vapor  which  it  took  up  when  warmed  in  the 
body.  We  therefore  conclude  that  air  when  breathed  gains 
water  vapor  and  carries  it  off  from  the  lungs.  The  quan- 
tity of  water  thus  removed  from  the  body  is  about  nine 
ounces  each  twenty-four  hours. 

Chemical  Changes. — The  most  important  changes 
brought  about  in  the  breathed  air  are  those  in  its  chemical 

What  changes  are  produced  in  the  air  on  its  being  once  breathed  ? 
How  does  expired  air  differ  in  temperature  from  inspired? 
How  does  expired  air  differ  from  inspired  in  moisture?    How 
much  water  is  evaporated  from  the  lungs  daily? 


252  THE  HUMAN  BODY, 

composition.     Pure  air  when  completely  dried  consists  in 
100  parts  of — 

By  Volume.  By  Weight. 

Oxygen 20.8  23 

Nitrogen 79.2  77 

When  breathed  once,  such  air  gains  rather  more  than 
4  volumes  in  100  of  carbon  dioxide,  and  loses  rather  more 
than  5  of  oxygen.  More  accurately,  100  volumes  of  ex- 
pired air,  when  dried,  consist  of — 

Oxygen 15.4 

Nitrogen ?L.  2 

Carbon  dioxide 4.3 

The  expired  air  also  contains  volatile  organic  substances 
in  quantities  too  minute  for  chemical  analysis,  but  readily 
detected  by  the  nose  upon  coming  into  a  close  room  in 
which  a  number  of  persons  have  been  collected. 

The  Quantity  of  Oxygen  taken  up  by  the  Lungs  in  a 
Day. — We  have  already  seen  that  the  quantity  of  air  breathed 
in  a  day  is  648,000  cubic  inches.  This  loses  5.4  per  cent, 
of  oxygen  or  35,000  cubic  inches,  weighing  12,818  grains 
(If  Ibs.):  the  body  therefore  gains  this  amount  of  that  gas 
through  the  lungs  daily. 

The  Amount  of  Carbon  Dioxide  passed  out  from  the 
Lungs  in  a  Day. — This  being  4.3  per  cent,  of  the  total  bulk 
of  the  air  breathed,  is  27,864  cubic  inches;  it  weighs  14,105 
grains  or  about  2  Ibs. 

We  thus  find  that  though  each  breath  seems  in  itself  a 

What  is  the  chemical  composition  of  pure  air  by  volume?    By 
weight?     What  substances  does  air  gain  and  lose  when  once  breathed? 
What  is  the  composition  by  volume  of  dried  expired  air?     Wlm'c 
does  dried  expired  air  contain  besides  oxygen,  nitrogen,  and  carbon 
dioxide  ? 

What  bulk  of  oxygen  does  the  air  breathed  in  a  day  lose?  What 
weight?  How  much  oxygen  does  the  body  take  up  daily  by  means 
of  the  lungs? 

What  bulk  of  carbon  dioxide  is  carried  off  by  breathing  in  each 
day?  What  does  it  weigh? 


VENTILATION.  253 

very  little  thing,  on  calculation  it  is  obvious  that  the  total 
amount  of  matter  received  into  the  body  from  the  lungs, 
and  that  passed  out  of  it  by  these  organs,  every  day  of  our 
lives  is  considerable.  In  a  year  each  adult  breathes  about 
10,000  Ibs.  of  air  ;  from  it  he  takes  657  Ibs.  of  oxygen,  and 
to  it  he  gives  off  730  Ibs.  of  carbon  dioxide. 

Changes  of  Volume  in  Air  once  breathed. — If  the  ex- 
pired air  be  measured  as  it  leaves  the  body  its  bulk  will  be 
found  greater  than  that  of  the  inspired  air,  since  it  not 
only  has  water  vapor  added  to  it,  but  is  expanded  in  con- 
sequence of  its  higher  temperature.  If,  however,  it  be  dried 
and  reduced  to  the  same  temperature  as  the  inspired  air, 
its  volume  will  be  found  diminished,  since  it  has  lost  5.4 
volumes  of  oxygen  for  every  4.3  volumes  of  carbon  dioxide 
which  it  has  gained. 

Ventilation. — Since  at  each  breath  some  oxygen  is  taken 
from  the  air  and  some  carbon  dioxide  given  to  it,  were 
the  atmosphere  around  a  living  man  not  renewed  he  would 
at  last  be  unable  to  get  from  the  air  the  oxygen  he  required; 
he  would  die  of  oxygen  starvation  or  be  suffocated,  as  such 
a  mode  of  death  is  called,  as  surely,  though  not  quite  so 
fast,  as  if  he  were  put  under  the  receiver  of  an  air-pump 
and  all  the  air  around  him  removed.  Hence  the  necessity 
of  ventilation  to  supply  fresh  air  in  place  of  that  breathed, 
and  clearly  the  amount  of  fresh  air  requisite  must  be  deter- 
mined by  the  number  of  persons  collected  in  a  room:  the 
supply  which  would  be  ample  for  one  person  would  be  in- 

Wliat  weight  of  air  is  breathed  yearly  by  an  adult?  How  much 
oxygen  is  taken  from  it?  How  much  carbon  dioxide  is  given  to  it? 

How  does  the  air  expired  differ  in  bulk  from  inspired?  Why? 
If  the  expired  air  be  dried  and  cooled  to  the  temperature  of  the  in- 
spired, what  is  found?  Why? 

Why  would  a  man  die  if  the  air  around  him  were  not  renewed? 
What  is  suffocation?  What  is  the  object  of  ventilation? 


254  THE  HUMAN  BODY. 

sufficient  for  two.  Moreover,  fires,  gas,  and  lamps  all  use 
up  the  oxygen  of  the  air  and  give  carbon  dioxide  to  it,  and 
hence  calculation  must  be  made  for  them  in  arranging  for 
the  ventilation  of  a  building  in  which  they  are  to  be  used. 

When  breathed  Air  becomes  unwholesome. — In  order 
that  air  be  unwholesome  to  breathe,  it  is  by  no  means 
necessary  that  it  shall  have  lost  so  much  of  its  oxygen  as  to 
make  it  difficult  for  the  body  to  get  what  it  wants  of  that 
gas.  The  evil  results  of  insufficient  air-supply  are  rarely 
directly  due  to  that  cause  even  in  the  worst  ventilated 
room,  for  the  blood  flowing  through  the  lungs  can  take 
what  oxygen  it  wants  from  air  containing  comparatively 
little  of  that  gas.  The  headache  and  drowsiness  which 
come  on  from  sitting  in  badly  ventilated  rooms,  and  the 
want  of  energy  and  general  ill-health  which  result  from 
permanently  living  in  such,  are  dependent  on  a  slow  poison- 
ing of  the  body  by  the  reabsorption  of  matters  eliminated 
from  the  lungs  in  previous  respirations.  What  these  are 
is  not  accurately  known;  they  doubtless  belong  to  those 
volatile  bodies  mentioned  above  as  carried  off  in  small 
quantities  in  each  breath,  since  observation  shows  that  the 
air  becomes  injurious  long  before  the  amount  of  carbon 
dioxide  in  it  is  sufficient  of  itself  to  do  any  harm.  Breath- 
ing air  containing  one  or  two  per  cent,  of  that  gas  produced 
by  ordinary  chemical  methods  does  no  particular  injury, 
but  the  breathing  of  air  containing  one  per  cent,  of  carbon 


What  conditions  determine  the  supply  of  fresh  air  which  should 
be  provided  to  a  room? 

Is  air  ever  unwholesome  wrhile  still  capable  of  supplying  the 
oxygen  which  the  body  requires?  What  results  from  living  in  ill- 
ventilated  rooms?  Why?  Does  air  once  breathed  become  injuri- 
ous before  the  quantity  of  carbon  dioxide  in  it  is  poisonous? 
What  percentage  of  pure  carbon  dioxide  may  be  present  in  the  air 
breathed  without  doing  harm? 


VENTILATION.  255 

dioxide  produced  by  respiration  is  decidedly  injurious, 
because  of  the  other  things  sent  out  of  the  lungs  along  with 
it.  Carbon  dioxide,  in  any  such  percentage  as  is  commonly 
found  in  a  room,  is  not  poisonous,  as  used  to  be  believed, 
but  as  it  is  tolerably  easily  estimated  in  air,  while  the  more 
dangerous  injurious  substances  evolved  in  breathing  are  not, 
the  purity  or  foulness  of  the  air  in  a  room  is  usually  deter- 
mined by  finding  the  percentage  of  carbon  dioxide  in  it; 
but  it  must  be  borne  in  mind  that  to  mean  much  this  car- 
bon dioxide  must  have  been  produced  by  breathing;  other- 
wise the  amount  of  it  present  is  no  guide  to  the  quantity 
of  the  more  important  poisonous  substances  present.  Of 
course  when  a  great  deal  of  carbon  dioxide  is  present  the 
air  is  irrespirable,  as  for  example  sometimes  at  the  bottom 
of  wells  or  brewing- vats. 

The  Quantity  of  Fresh  Air  which  should  be  allowed  for 
each  Person  in  a  Boom. — In  each  minute  a  man  breathes 
out  450  cubic  inches  of  air  containing  rather  more  than 
4  per  cent,  of  carbon  dioxide.  This  mixed  with  three  times 
its  bulk  of  pure  air  would  give  a  little  over  one  cubic 
foot  containing  one  per  cent,  of  carbon  dioxide.  Such  air 
is  no  longer  respirable  with  safety.  The  result  of  breath- 
ing it  for  an  hour  or  two  is  headache  and  drowsiness;  of 
breathing  it  for  weeks  or  months  several  hours  daily,  a 

What  percentage  of  carbon  dioxide  produced  by  breathing  shows 
that  the  air  is  unfit  for  use?  Is  the  proportion  of  carbon  dioxide 
found  ordinarily  in  a  room  poisonous?  Why  is  the  percentage 
of  carbon  dioxide  in  air  usually  employed  in  deciding  whether 
the  air  is  fit  to  breathe?  What  must  be  borne  in  mind  in  deciding 
from  the  percentage  of  carbon  dioxide  in  it  that  air  is  no  longer 
wholesome?  Is  air  containing  much  carbon  dioxide  fit  to  breathe? 
Give  an  example. 

What  bulk  of  air  does  a  man  contaminate  with  carbon  dioxide  to 
the  extent  of  one  per  cent,  in  each  minute?  Is  air  so  contaminated 
fit  to  breathe?  What  are  the  consequences  of  breathing  it  for  a  few 
hours?  What  of  breathing  it  for  months? 


256  THE  HUMAN  BODY. 

lowered  tone  of  the  whole  body,  less  power  of  work,  physi- 
cal or  mental,  and  less  power  of  resisting  disease.  The  ill 
effects  may  not  show  themselves  at  once,  and  may  accord- 
ingly be  overlooked  or  considered  scientific  whims  by  the 
careless,  but  they  are  there  ready  to  manifest  themselves 
nevertheless. 

In  order  to  have  air  to  breathe  in  a  fairly  pure  state 
every  man  should  have  for  his  own  allowance  at  least  about 
800  cubic  feet  of  space  to  begin  with,  and  the  arrangements 
for  ventilation  should  at  the  very  least  renew  this  at  the 
rate  of  one  cubic  foot  per  minute.  The  nose  is,  however, 
the  best  guide,  and  it  is  found  that  at  least  five  times  this 
supply  of  fresh  air  is  necessary  to  keep  free  from  any  odor 
the  room  inhabited  by  one  adult.  If  an  inhabited  room 
smells  " close"  to  one  coming  into  it  from  "out  of  doors," 
the  air  in  it  is  unwholesome  to  breathe  for  any  length  of 
time. 

How  to  Ventilate. — Ventilation  does  not  necessarily 
mean  draughts  of  cold  air,  as  is  too  often  supposed.  In 
warming  by  indirect  radiation  it  may  readily  be  secured  by 
fixing,  in  addition  to  the  registers  from  which  the  fresh 
warmed  air  reaches  the  room,  corresponding  openings  at 
the  opposite  side  by  which  the  old  air  may  pass  off  to  make 
room  for  the  new.  An  open  fire  in  a  room  will  always 
keep  up  a  current  of  air  through  it,  and  is  one  of  the 
most  wholesome,  though  not  most  economical,  methods  of 
warming  an  apartment. 

Why  are  the  injurious  effects  of  impure  air  apt  to  be  ignored? 

What  volume  of  air  should  be  allowed  to  each  adult?  At  what 
rate  should  it  be  replenished?  What  supply  of  fresh  air  is  needed  to 
keep  an  inhabited  room  free  from  odor?  Is  it  safe  to  live  in  a  room 
which  "  smells  close"? 

How  may  ventilation  be  secured  in  heating  by  "indirect  radia- 
tion"? What  are  the  advantages  and  what  the  disadvantages  of  an 
open  fire? 


CHANGES  OF  BLOOD  IN  THE  L  UNGS.     257 

Stoves  in  a  room  unless  constantly  supplied  with  fresh 
air  from  without  dry  its  air  to  an  unwholesome  extent.  If 
no  appliance  for  providing  this  supply  exists  in  a  room  it 
can  usually  be  got,  without  a  draught,  by  fixing  a  board 
about  four  inches  wide  under  the  lower  sash  and  shutting 
the  window  down  on  it.  Fresh  air  then  comes  in  by  the 
opening  between  the  two  sashes  and  in  a  current  directed 
upwards,  which  gradually  diffuses  itself  over  the  room 
without  being  felt  as  a  draught  at  any  one  point.  In  the 
method  of  heating  by  direct  radiation  the  apparatus  .em- 
ployed provides  of  itself  no  means  of  drawing  fresh  air  into 
a  room,  as  the  draught  up  the  chimney  of  an  open  fire- 
place or  of  a  stove  does;  and  therefore  special  inlet  and 
outlet  openings  are  very  necessary.  Since,  fortunately, 
few  doors  and  windows  fit  quite  tight,  fresh  air  gets  into 
closed  rooms  in  tolerable  abundance  for  one  or  two  in- 
habitants. 

Changes  undergone  by  the  Blood  in  the  Lungs. — These 
are  the  exact  reverse  of  those  exhibited  by  the  breathed  air 
— what  the  air  gains  the  blood  loses,  and  vice  versa.  The 
blood  loses  heat,  and  water,  and  carbon  dioxide, in  the  pul- 
monary capillaries,  and  gains  oxygen.  These  gains  and 
losses  are  accompanied  by  a  change  of  color  from  the  dark 
purple  which  the  blood  exhibits  in  the  pulmonary  artery, 
to  the  bright  scarlet  it  possesses  in  the  pulmonary  veins. 

Why  the  Blood  changes  its  Color  as  it  flows  through 

What  are  stoves  apt  to  do?  Point  out  a  good  way  of  supplying 
fresh  air  to  a  room  warmed  by  a  stove?  What  are  especially  impor- 
tant in  a  room  heated  by  "direct  radiation"?  Why  is  it  fortunate 
that  doors  and  windows  do  not  fit  air-tight? 

What  is  the  relationship  between  the  gains  and  losses  of  blood  in 
the  pulmonary  circulation,  and  the  losses  and  gains  of  the  breathed 
air?  What  does  the  blood  lose  as  it  flows  through  the  lungs?  What 
does  it  gain?  What  change  in  the  color  of  the  blood  accompanies 
these  sains  and  losses? 


258  THE  HUMAN  BODY. 

the  Pulmonary  Capillaries. — The  color  of  the  blood  depends 
on  its  red  corpuscles,  since  pure  blood-plasma  or  blood- 
serum  is  colorless  or  at  most  a  very  faint  straw  yellow. 
Hence  the  color  change  which  the  blood  experiences  in 
circulating  through  the  lungs  must  be  due  to  some  change 
in  its  red  corpuscles.  These  consist  chiefly  of  Jicemoglobiri 
(p.  178),  and  haemoglobin,  as  we  have  learned,  is  a  sub- 
stance which  has  the  power  of  absorbing  oxygen  and  form- 
ing a  bright  scarlet  compound  called  oxylicemogloUn. 
This  oxyhaemoglobin  very  easily  gives  up  its  oxygen  when 
it  is  placed  under  conditions  where  that  gas  is  scarce:  the 
haemoglobin  left  behind  has  a  dark  purple  color.  The 
blood  leaving  the  lungs  by  the  pulmonary  veins  is  bright 
red  because  all  its  haemoglobin  has  been  turned  into  oxy- 
haemoglobin. From  the  left  side  of  the  heart  it  is  conveyed 
by  the  branches  of  the  aorta  to  all  the  organs  of  the  body. 
These  are  constantly  using  oxygen,  which  is  therefore  very 
scarce  in  them,  and  as  the  blood  flows  through  its  oxy- 
haemoglobin is  broken  up,  the  oxygen  taken  away,  and 
dark  purple-red  haemoglobin  left  to  be  conveyed  by  the 
veins  to  the  right  auricle  of  the  heart.  From  there  it 
passes  to  the  right  ventricle  and  thence  by  the  pulmonary 
artery  to  the  lungs,  where  it  again  picks  up  oxygen  and 

Why  must  the  change  in  color  of  the  blood  during  its  pulmonary 
circuit  be  due  to  a  change  in  its  red  corpuscles?  What  is  the  chief 
constituent  of  the  red  blood-corpuscles?  What  property  does  haemo- 
globin possess  with  reference  to  oxygen?  What  is  the  color  of  oxy- 
haemoglobin? 

When  does  oxyhaemoglobin  give  off  its  oxygen?  What  is  the 
color  of  haemoglobin?  Why  is  the  blood  in  the  pulmonary  veins 
bright  red?  Where  is  it  conveyed?  Why  is  oxygen  scanty  in  most 
organs  of  the  body?  What  results  as  regards  the  oxy haemoglobin  of 
the  blood?  What  is  the  color  of  the  blood  sent  to  the  right  auricle 
of  the  heart?  What  is  the  subsequent  course  of  this  blood  until  it 
reaches  the  lungs?  What  does  it  receive  in  the  lungs?  How  is  its 
color  altered  in 'those  organ <? 


APPENDIX.  259 

becomes  bright-red  oxyhaBmoglobin.     The  red  corpuscles 
of  the  blood  are  so  many  little  boxes  in  which  oxygen  is 
packed  away  in  the  lungs  for  conveyance  to  distant  parts 
of  the  body. 
What  is  the  function  of  the  red  blood-corpuscles? 


APPENDIX  TO  CHAPTER  XVIL 

1.  To  show  that  air  is  warmed  by  breathing,  breathe  for  a  few 
seconds  on  the  bulb  of  a  thermometer.     The  mercury  will  be  seen  to 
rise  rapidly  in  its  stem. 

2.  To  demonstrate  that  air  gains  water  in  the  lungs,  breathe  on  a 
mirror,  or  on  a  knife-blade  or  other  polished  metallic  surface. 

3.  The  presence  of  carbon  dioxide  in  expired  air  may  be  readily 
demonstrated  by  expiring  through  a  tube  immersed  in  lime-water. 
This  may  be  obtained  at  any  drug-store;  with  carbon  dioxide  it  gives 
a  white  precipitate,  which  dissolves  readily  in  a  little  vinegar. 

4.  To  show  that  much  less  carbon  dioxide  exists  in  inspired  air, 
take  a  small  bottle  with  a  wide  neck.  Fit  tightly  into  the  neck  of  the 
bottle  a  cork  perforated  by  two  holes.  Through  one  hole  pass  a  glass 
tube  reaching  to  near  the  bottom  of  the  bottle,  and  through  the  other 
one  which  ends  just  below  the  cork;  on  the  outer  end  of  this  tube  fit 
a  foot  or  so  of  rubber  tubing.     Remove  the  cork;  half  fill  the  bottle 
with  lime-water  and  then  replace  the  cork.     Suck  air  through  the 
rubber  tubing.     It  will  bubble  through  the  lime-water,  but  (unless 
the  room  is  very  badly  ventilated)  a  great  deal  must  be  drawn  through 
the  lime-water  before  as  abundant  a  precipitate  is  produced  as  that 
which  results  from  blowing  a  small  quantity  of  breathed  air  (3) 
through  the  lime-water. 

5.  The  influence  of  oxygen  upon  the  color  of  the  blood  may  be 
illustrated  as  follows: 

a.  Take  to  a  slaughter-house  a  glass  jar  or  beaker  (an  ordinary 
tumbler  answers  quite  well),  two  bottles,  an  earthenware  quart  pitcher, 
and  a  bundle  of  wire. 

b.  When  an  animal  is  killed  and  bled,  collect  some  blood  in  the 
jar  and  let  it  clot. 

c.  Collect  some  more  blood  in  the  pitcher,  and  defibrinate  by 


260  THE  HUMAN  BODY. 

thorough  whipping  with  the  bundle  of  wire.     Half  fill  each  bottle 
with  the  defibrinated  blood;  then  cork  the  bottles. 

d.  Having  brought  home  all  the  specimens,  set  them  aside  until  the 
next  morning  in  a  cool  place.     It  will  then  be  found  that  the  blood 
in  each  bottle  is  dark-colored  or  venous  (having  used  up  its  own 
oxygen  and  not  being  able  to  get  more  from  the  air),  and  that  the 
clot  in  the  jar  is  bright  scarlet  (arterial-colored)  above  where  it  is  in 
contact  with  the  air,  but  dark  purple-red  where  it  is  immersed  in 
the  serum. 

e.  Invert  the  clot :  in  an  hour  or  two  its  previously  dark  original 
under  surface  will  have  become  bright  red,  while  the  original  upper 
surface,  previously  bright-colored  and  now  immersed  in  the  serum 
away  from  the  air,  will  have  become  venous  in  tint. 

/.  Take  the  cork  out  of  one  bottle;  renew  the  air  in  it  by  blow- 
ing. Placing  a  thumb  on  the  neck  of  the  bottle,  thoroughly  shake 
up  the  blood  with  the  air.  Then  renew  the  air  again,  and  shake  once 
more;  and  so  on  for  three  or  four  times.  At  the  end  the  blood  shaken 
up  with  air  will  be  seen  to  have  assumed  a  much  brighter  red  color 
than  that  kept  shut  up  in  the  other  bottle. 

ff.  If  the  proper  chemical  apparatus  and  reagents  are  accessible, 
the  air  in  the  bottle  about  to  be  shaken  may  be  replaced  by  nitrogen, 
hydrogen,  or  pure  oxygen,  and  the  procedures  described  in  section 
/repeated.  It  will  be  found  that  only  the  oxygen  brightens  the 
blood  color.  As  any  one  possessing  the  chemical  apparatus  and 
knowledge  implied  for  the  execution  of  this  experiment,  will  certainly 
know  how  to  replace  the  air  by  the  gases  above  named,  no  further 
details  need  be  given. 


CHAPTER  XVIII. 

THE   KIDNEYS  AND  THE   SKIN. 

General  Arrangement  of  the  Nitrogen-excreting  Or- 
gans.— These  organs  are  (1)  the  kidneys,  the  glands  which 
secrete  the  urine;  (2)  the  ureters  or  ducts  of  the  kidneys, 
which  carry  the  secretion  to  (3)  the  urinary  bladder,  a 
reservoir  in  which  it  accumulates  and  from  which  it  is  ex- 
pelled from  time  to  time  through  (4)  an  exit  tube,  the 
urethra.  The  general  arrangement  of  these  parts,  as  seen 
from  behind,  is  shown  in  Fig.  73.  The  kidneys,  R,  lie 
at  the  back  of  the  abdominal  cavity,  opposite  the  upper 
lumbar  vertebrae,  one  on  each  side  of  the  middle  line. 
Each  is  a  solid  mass,  with  a  convex  'outer  and  a  concave 
inner  border,  and  its  upper  end  a  little  larger  than  the 
lower.  From  the  abdominal  aorta,  A,  a  renal  artery,  Ar, 
enters  the  inner  border  of  each  kidney,  to  break  up  within 
it  into  finer  branches,  ultimately  ending  in  capillaries. 
The  blood  is  collected  from  these  into  the  renal  veins,  Vr, 
one  of  which  leaves  each  kidney  and  opens  into  the  inferior 
vena  cava,  Vc,  which  carries  it,  after  having  lost  water  and 
urea  in  the  kidney,  back  to  the  heart.  From  the  concave 

Name  the  chief  organs  concerned  in  removing  from  the  body  its 
nitrogenous  waste  matters.  Describe  the  general  arrangement  of 
these  organs.  Describe  the  form  of  a  kidney.  What  vessel  supplies 
it  with  blood?  What  vessel  carries  blood  out  of  the  kidney?  What 
has  the  blood  carried  off  from  a  kidney  lost  while  flowing  through 
that  organ? 

[261] 


262 


THE  HUMAN  BODY. 


FIG.  73.-The  renal  organs,  viewed  from  behind.  R,  right  kidney;  A.  . 
Ar,  right  renal  artery;  Fc,  inferior  vena  cava;  Fr,  right  renal  vein-  U  right 
ureter;  Vu,  bladder;  Ua,  commencement  of  urethra. 


STRUCTURE  OF  THE  KIDNEYS.  263 

border  of  each  kidney  proceeds  also  the  ureter,  U,  a  slender 
tube  opening  below  into  the  bladder,  Vu,  near  its  lower 
end.  From  the  bladder  proceeds  the  urethra,  at  Ua.  The 
channel  of  each  ureter  passes  very  obliquely  through  the 
wall  of  the  bladder;  accordingly  if  the  pressure  inside  the 
latter  organ  rises  above  that  of  the  liquid  in  the  ureter  the 
walls  of  the  oblique  passage  are  pressed  together  and  it  is 
closed.  Usually  the  bladder  (which  contains  muscular 
tissue  in  its  walls)  is  relaxed,  and  the  urine  flows  readily 
into  it  from  the  ureters.  The  commencement  of  the 
urethra  being  kept  closed  by  elastic  tissue  around  it  (which 
can  voluntarily  be  reinforced  by  muscles  which  compress 
the  tube),  the  urine  accumulates  in  the  bladder.  When 
this  latter  contracts  and  presses  on  its  contents  the  ureters 
are  closed  in  the  way  above  indicated,  the  elasticity  of  the 
fibres  closing  the  urethral  exit  from  the  bladder  is  over- 
come, and  the  liquid  is  forced  out. 

Naked  Eye  Structure  of  the  Kidneys. — When  a  section 
is  made  through  a  kidney  from  its  outer  to  its  inner  border 
(Fig.  74)  it  is  seen  that  a  deep  fissure,  the  hihis,  leads 
into  the  latter.  In  the  liilus  the  ureter  widens  out  to  form 
the  pelvis  of  the  kidney,  which  breaks  up  into  a  number  of 
smaller  divisions,  the  cups  or  calices.  The  cut  surface  of 
the  kidney  proper  is  seen  to  consist  of  two  distinct  parts; 
an  outer  or  cortical  portion,  and  an  inner  or  medullary. 
The  medullary  portion  is  less  red  and  more  glistening  to 
the  eye,  is  finely  striated  in  a  radial  direction,  and  does  not 

What  is  the  ureter?  Under  what  circumstances  is  its  opening 
into  the  bladder  closed?  What  is  the  usual  state  of  things? 
How  is  the  commencement  of  the  urethra  closed?  What  results? 
What  happens  when  the  bladder  contracts? 

What  is  seen  on  a  section  made  through  a  kidney?  How  is  the 
'pelvis  of  the  kidney  formed?  What  are  the  calices?  What  is  seen 
on  the  cut  surface  of  the  kidney  proper?  How  does  the  medullary 
part  differ  in  appearance  from  the  cortical? 


264 


THE  HUMAN  BODY. 


consist  of  one  continuous  mass,  but  of  a  number  of  conical 
portions,  the  pyramids  of  Malpiffhi,  %',  each  of  which  is 


FIG.  74.— Section  through  the  right  kidney  from  its  outer  to  its  inner  border. 
1,  cortex;  2,  medulla;  2',  pyramid  of  Malpighi;  2",  pyramid  of  Ferrein:  5,  small 
branches  of  the  renal  artery  entering  between  the  pyramids;  A,  a  branch  of  the 
renal  artery;  C,  the  pelvis  of  the  kidney;  U,  ureter;  C,  a  calyx. 

separated  from  its  neighbors  by  a  prolongation,*,  of  the 

cortical  substance.     This,  however,  does  not  reach  to  the 

Describe  the  pyramids  of  Malpighi.     What  lies  between  them? 


MINUTE  STRUCTURE  OF  THE  KIDNEY.          265 

apex  of  the  pyramid,  which  projects,  as  the  papilla,  into  a 
calyx  of  the  ureter.  At  its  outer  end  each  pyramid  separates 
into  smaller  portions,  2",  separated  by  thin  layers  of  cortex 
and  gradually  spreading  everywhere  into  the  latter.  The 
cortical  substance  is  redder,  more  granular  looking,  and 
less  shiny  than  the  medullary;  it  forms  everywhere  the 
outer  layer  of  the  organ,  besides  dipping  in  between  the 
pyramids  in  the  manner  above  described. 

The  renal  artery  divides  in  the  hilus  into  branches  (5) 
which  run  into  the  kidney  substance  between  the  pyra- 
mids, give  off  a  few  twigs  to  the  pyramids,  and  end  finally 
in  a  much  closer  vascular  network  in  the  cortex. 

The  Minute  Structure  of  the  Kidney. — The  kidneys  are 
compound  tubular  glands,  being  composed  of  branched 
microscopic  uriniferous  tubules,  lined  by  a  single  layer  of 
secreting  cells,  supported  by  connective  tissue,  and  supplied 
with  blood-vessels,  nerves,  and  lymphatics.  The  final 
branches  of  each  tubule  end  in  a  dilatation  which  contains 
a  knot  of  blood-vessels,  through  whose  walls  water  and 
salts  filter  into  the  tubule.  As  the  water  trickles  along  the 
latter,  the  cells  lining  it  pass  out  the  nitrogenous  wastes 
of  the  blood  brought  there  by  the  capillaries  which  wrap 
closely  around  them.  The  tubules  unite  in  the  pyramids 
to  form  fewer  and  larger  ducts,  which  pour  the  secretion 

How  does  the  apex  of  a  pyramid  end?  Where  do  we  find  the  cor- 
tical substance  of  the  kidney? 

Describe  the  general  distribution  of  the  renal  artery  and  its 
branches  in  the  kidney.  Wliat  part  of  the  kidney  contains  most 
capillary  biood- vessels? 

To  what  type  of  gland  do  the  kidneys  belong?  Of  what  are  they 
'made  up?  How  do  the  uriniferous  tubules  end?  What  lies  in  each 
dilatation?  What  niters  from  the  blood-vessels  of  its  dilatation  into 
the  cavity  of  the  tubule?  What  is  added  to  this  as  it  trickles  along 
the  tubule?  How  is  the  nitrogenous  waste  of  the  body  brought  close 
to  the  kidney  tubules?  What  becomes  of  the  tubules  in  the  pyra- 
mids? Where  do  the  larger  ducts  convey  the  secretion? 


266  THE  HUMAN  BODY. 

into  the  calices  of  the  pelvis  of  the  ureter,  and  this  tube 
then  conveys  it  to  the  bladder. 

The  Renal  Secretion  is  less  in  bulb  in  warm  weather, 
when  perspiration  carries  off  a  good  deal  of  the  excess 
water  of  the  blood,  than  in  cold.  On  an  average  the  kid- 
neys eliminate  from  the  body  in  twenty-four  hours  about 
fifty  ounces  (2£  pints)  of  water,  and  500  grains  (1^  ounces) 
of  urea,  which  contain  a  little  more  than  230  grains  of 
nitrogen. 

The  Kidneys,  being  the  chief  organs  for  the  excretion 
of  nitrogen,  are  among  the  most  important  organs  of  the 
body.  Any  defect  in  their  healthy  activity  leads  to  serious 
interference  with  the  working  of  many  organs,  due  tu  the 
accumulation  in  the  body  of  nitrogenous  waste  products.* 

The  Skin,  which  covers  the  whole  exterior  of  the  body, 
consists  everywhere  of  two  distinct  layers:  an  outer,  the 
cuticle  or  epidermis;  and  a  deeper,  the  dermis,  cutis  vera, 
or  corium.  A  blister  is  due  to  the  accumulation  of  liquid 
between  these  two  layers.  Hairs  and- nails  are  excessively 
developed  parts  of  the  epidermis. 

The  Epidermis,  Fig.  75,  consists  of  cells,  arranged  in 

Where  does  the  ureter  convey  it? 

Is  the  bulk  of  the  renal  secretion  greater  in  summer  or  in  winter? 
Why?  What  is  its  average  daily  amount?  How  much  urea  does  it 
contain?  How  much  nitrogen  is  contained  in  this  quantity  of  urea? 

Why  are  the  kidneys  important  organs?  What  follows  when 
their  physiological  work  is  defective? 

Of  what  two  main  part*  does  the  skin  consist?  What  is  a  blister? 
What  are  hairs  and  nails? 

*  Bright1  s  Disease,  one  of  the  commonest  and  most  dangerous  of  maladies, 
consists  essentially  in  an  alteration  of  the  kidney  structure,  in  consequence  of 
which  these  organs  cease  to  eliminate  urea  from  the  blood,  and  drain  off  pure 
albumen  from  it  instead.  The  three  most  common  causes  of  Bright's  disease 
are  (1)  an  acute  illness,  as  scarlet  fever,  of  which  it  is  a  frequent  result;  (2)  sud- 
den exposure  to  cold  when  warm  (this  often  drives  blood  in  excessive  amount 
f  rom  the  skin  to  internal  organs  and  leads  to  k;dney  disease) ;  and  (3)  excessive 
drinking  of  alcoholic  liquids. 


THE  CORIUM. 


269 


tissue  forming  an  insoluble  and  tough  compound  with  the 
tannin  of  the  oak-bark  employed.  Wherever  there  are 
hairs  bundles  of  plain  muscular  tissue  are  found  in  the 
corium;  it  contains  also  a  close  network  of  capillary  blood- 


FiG.76.— A  section  through  the  skin  and  subcutaneous  areolar  tissue,  a,  horny 
stratum,  and  6,  Malpighian  layer  of  the  epidermis;  c,  dermis,  passing  belo-sv 
into,  d,  loose  areolar  tissue,  with  fat,/,  in  its  meshes:  above,  dermic  papillae  are 
seen,  projecting  into  the  epidermis  which  is  moulded  on  them,  i,  opening  of  a 
sweat-gland;  h,  duct  of  ditto;  g,  the  gland  itself. 

vessels,  and  numerous  lymphatics  and  nerves.  In  shaving, 
as  long  as  the  razor  keeps  in  the  epidermis  there  is  no 
bleeding;  but  a  deeper  cut  shows  at  once  the  presence  of 
blood-vessels  in  the  true  skin. 

How?    Where  do  we  find  plain  muscular  tissue  in  the  corium? 

blood- vessels  are  found  iu  it?    What  ejse? 


270  •      THE  HUMAN  BODY. 

The  Papillae  of  the  Dermis.— The  outer  surface  of  the 
corium  is  almost  everywhere  raised  into  minute  elevations, 
called  papillce,  on  which  the  epidermis  is  molded,  so  that 
its  deep  side  presents  pits  corresponding  to  the  projec- 
tions of  the  dermis.  In  Fig.  75  is  shown  a  papilla  of  the 
corium  containing  a  knot  of  blood-vessels,  supplied  by  the 
small  artery,  /,  and  having  the  blood  carried  off  from  them 
by  the  two  little  veins,  gg.  Other  papillae  contain  no 
capillary  loops,  but,  instead,  special  organs  connected  with 
nerve-fibres,  and  supposed  to  be  concerned  in  the  sense  of 
touch.  On  the  palm  of  the  hand  the  dermic  papillae  are 
especially  well  developed  (as  they  are  in  most  parts  where 
the  sense  of  touch  is  acute),  and  are  frequently  compound 
or  branched  at  the  tip.  On  this  surface  of  the  hand  they 
are  arranged  in  rows;  the  epidermis  fills  up  the  hollows 
between  the  papillae  of  the  same  row,  but  dips  down  be- 
tween adjacent  rows,  and  thus  are  produced  the  finer  epi- 
dermic ridges  seen  on  the  palms.*  The  wrinkles  of  old 
persons  are  due  to  the  absorption  of  subcutaneous  fat  and 
of  other  soft  parts  beneath  the  skin,  which,  not  shrinking 
itself  to  the  same  extent,  is  thrown  into  folds. 

Hairs,  longer  or  shorter,  are  found  all  over  the  surface 
of  the  body,  except  in  a  few  regions,  as  the  palms  of  the 
hands  and  the  soles  of  the  feet.  A  hair  is  a  slender  thread 
of  epidermis,  developed  on  a  special  dermic  papilla  placed 

What  are  the  papillae  of  the  epidermis?  "Describe  a  papilla  con- 
taining blood-vessels.  What  is  found  in  other  papillae?  Name  a 
region  of  the  skin  where  the  dermic  papillae  are  especially  de- 
veloped. How  are  the  ridges  seen  on  the  palm  of  the  hand  pro- 
duced? To  what  are  the  wrinkles  on  the  skin  of  elderly  persons 
due? 

Name  regions  of  the  skin  which  have  no  hairs.  What  is  a 
hair? 

*  The  more  marked  furrows  on  the  palm,  the  so-called  "lines  of  life"  of 
the  gypsy's  palmistry,  have  a  different  origin, 


THE  NAILS. 


271 


at  the  bottom  of  a  depression,  formed  by  a  pitting-in  of  the 

dermis.     The  depression  is  known  as  the  hair  follicle.     The 

part  of  the  hair  buried  in  the 

follicle  is   called   its  root;  this 

is   succeeded  by  a  stem,  which 

(in  uncut  hairs)  tapers  off  to   a 

point.     Each  hair  is  made  up 

of  a  number  of  epidermic  cells, 

arranged  together  so  as  to  form 

a  fibre. 

Nails. — A  nail  is  a  part  of 
the  epidermis,  with  its  horny 
stratum  greatly  developed.  The 
back  part  of  the  nail  fits  into 
a  furrow  of  the  dermis,  and  is 
called  its  root.  The  visible  part 
consists  of  a  body,  attached  to 
the  dermis  beneath  (which  forms 
the  bed  of  the  nail),  and  of  a 
free  edge.  Near  the  root  is  a 
little  area,  whiter  than  the  rest 
of  the  nail,  called  the  lunula. 
The  whiteness  is  due  in  part  to 
the  nail  being  really  more 
opaque  there,  and  partly  to  the 
fact  that  its  bed,  which  seen 
through  the  nail  causes  its  pink 
color,  is  in  this  region  less  vas- 
cular. 

The  portion  of  the  corium  on  which  the  nail  is  formed 

What  is  a  hair  follicle?    What  is  the  root  of  a  hair?    The  stem? 
Of  what  is  a  hair  composed? 

What  is  a  nail?    Of  what  parts  does  it  consist?    What  is  the 
lunula?    Why  is  it  paler  in  color  than  the  rest  of  the  nail? 


FIG.  77.— The  root  of  a  hair  iro 
bedded  in  its  follicle,  o,  stem  of 
hair  cut  short;  o,  6,  root  of  hair; 
c,  swollen  part  of  root  which  fits 
on  z,  the  dermic  papilla  at  the 
bottom  of  the  hair  follicle;  n,  m,  Z, 
layer  of  skin  which  turn  in  to  line 
arid  form  the  follicle;  fc.  k,  mouths 
of  ducts  of  sebaceous  glands. 


272 


THE  HUMAN  BODY. 


is  called  its  matrix.  Behind,  this  forms  a  groove  lodging 
the  root  of  the  nail,  and  it  is  by  new  cells  added  there  that 
the  nail  grows  in  length.  The  part  of  the  matrix  lying 
beneath  the  body  of  the  nail,  and  called  its  bed,  is  highly 
vascular;  new  cells  formed  on  its  bed  and  added  to  its 
under  surface  cause  the  nail  to  increase  in  thickness,  as  it 
is  pushed  forward  by  the  new  growth  at  its  root.  The 
free  end  of  a  nail  is  therefore  its  thickest  part.  If  a  nail 
is  "cast"  in  consequence  of  an  injury, 
or  torn  off,  a  new  one  is  produced,  pro- 
vided the  matrix  is  not  destroyed. 

The  Glands  of  the  Skin  are  of  two 
kinds.     The  sweat  glands  or  sudori- 
parous glands,  and  the  oil  glands  or 
sebaceous  glands. 

The  Sweat  Glands  (Fig.  78)  are 
microscopic  tubes  which  reach  from 
the  surface  of  the  skin  to  the  subcu- 
taneous areolar  tissue;  then  the  tube 
often  branches,  and  is  coiled  up  into 
a  little  knot,  intertwined  with  blood 
capillaries.  These  glands  are  found  all 

I 

'  chMaipighTaen  over  tlie  skiri>  bufc  are  most  abundant  on 
the  palms  of  the  hands,  the  soles  of  the 
feet,  and  the  brow.   Altogether,  there  are 
about  two  and  a  half  millions  of  them. 
The  perspiration  or  sweat  poured  out  by  the  sudoriparous 


FIG.  ?8.—  A    sweat 


What  is  the  matrix  of  a  nail?  When  does  the  nail  grow  longer? 
What  is  the  bed  of  a  nail?  How  does  a  nail  grow  thicker?  Which 
is  its  thickest  part?  What  is  necessary  in  order  that  a  "  cast  nail" 
may  be  reproduced  ? 

What  glands  are  found  in  the  skin?  Describe  a  sweat  gland. 
Where  are  the  sweat  glands  most  numerous?  How  many  are  there 
on  the  whole  skin? 


THE  PERSPIRATION.  273 

glands  is  a  transparent  colorless  liquid,  with  a  peculiar  odor, 
varying  in  different  races,  and  in  the  same  individual  in 
different  regions  of  the  body.  Its  quantity  in  twenty-four 
hours  is  subject  to  great  variations,  but  usually  lies  between 
10,850  and  31,000  grains  (or  25  and  71  ounces).  The 
amount  is  influenced  mainly  by  the  surrounding  tempera- 
ture, being  greater  when  this  is  high;  but  _  it  is  also  in- 
creased by  other  things  tending  to  raise  the  temperature 
of  the  body,  as  muscular  exercise.*  The  sweat  may  or 
may  not  evaporate  as  fast  as  it  is  secreted;  in  the  former 
case  it  is  known  as  insensible,  in  the  latter  as  sensible  per- 
spiration. By  far  the  most-passes  off  in  the  insensible  form, 
drops  of  sweat  only  accumulating  when  the  secretion  is  very 
profuse,  or  the  surrounding  atmosphere  is  so  humid  that  it 
does  not  readily  take  up  more  moisture.  The  perspiration 
in  1000  partsx  contains  990  of  water  to  10  of  solids.  Among 
the  latter  is,  in  health,  a  little  urea,  some  sodium  chloride, 
and  otheivsalts.  In  diseased  conditions  of  the  kidneys  the 
urea  may  be  greatly  increased,  the  skin  supplementing  to  a 
certain  extent  deficiencies  of  those  organs. 

The  Sebaceous  Glands  nearly  always  open  into  hair  fol- 
licles. They  are  small  compound  racemose  glands  (p.  131). 
Each  presents  a  duct,  opening  near  the  mouth  of  the  hair 
follicle;  when  followed  back  this  duct  is  found  to  divide 
into  several  branches  which  end  in  globular  expansions. 

Describe  the  perspiration.  How  much  is  secreted  daily?  Point 
out  conditions  influencing  its  amount.  What  is  meant  by  "  insensi- 
ble perspiration"?  Under  what  conditions  do  we  find  "sensible 
perspiration"?  What  percentage  of  solids  exists  in  the  sweat? 
What  do  they  contain?  When  is  the  proportion,  of  urea  in  the 
perspiration  apt  to  be  increased? 

Where  do  the  sebaceous  glands  open?  To  what  type  of  gland  do 
they  belong? 

*  In  fever  the  sweat  glands  are  paralyzed,  and  we  find  a  high  temperature 
of  the  body  with  a  dry  skin. 


274  THE  HUMAN  BODY. 

The  latter  are  lined  by  secreting  cells.  The  mouths  of  the 
ducts  of  a  pair  of  sebaceous  glands  are  seen  on  the  sides 
of  the  hair  follicle  in  Fig.  77. 

The  Sebaceous  Secretion  is  oily  and  semi-fluid.  In  healthy 
persons  it  lubricates  the  hairs  and  renders  them  glossy  even 
when  no  "  hair-oil  "  is  used.  It  is  also  spread  more  or  less 
over  all  the  surface  of  the  skin,  and  makes  the  cuticle  less 
permeable  by  water,  which  in  consequence  does  not  readily 
wet  the  healthy  skin,  but  runs  off  it,  as  "off  a  duck's  back," 
though  to  a  less  marked  extent. 

The  Skin  as  a  Sense  Organ. — Besides  its  functions  as  a 
protective  covering  and  an  excretory  organ,  the  skin  is  of 
extreme  importance,  as  being  the  seat  of  one  of  our  most 
important  senses — the  sense  of  touch.  In  this  relationship 
it  will  be  considered  later  (Chap.  XXI). 

Hygiene  of  the  Skin. — The  sebaceous  secretion  and  the 
solid  residue  left  by  evaporating  sweat  form  a  solid  film 
over  the  skin,  which  tends  to  choke  the  mouths  of  the  sweat 
glands  (the  so-called  "pores"  of  the  skin)  and  impede  their 
action.  Yet  these  glands,  minute  though  each  is,  have  for 
their  function  to  separate  daily  from  the  body  a  great  amount 
of  water*  and  some  little  urea  and  salines.  Hence  the 
importance  of  personal  cleanliness.  The  whole  skin,  except 
that  of  the  scalp,  should  be  washed  daily.  Women  cannot 

Describe  the  structure  of  a  sebaceous  gland. 

Describe  the  sebaceous  secretion.  Why  is  the  hair  of  a  healthy 
person,  using  no  hair-oil,  glossy?  Why  does  water  run  off  the  skin? 

Enumerate  the  chief  functions  of  the  skin. 

How  are  the  mouths  of  the  sweat  glands  apt  to  be  choked  up? 
Point  out  functions  of  these  glands? 

How  much  of  the  skin  should  be  washed  daily? 

*  The  sweat  glands  not  merely  carry  off  some  water  from  the  body,  but  serve 
also  to  regulate  its  temperature.  When  water  evaporates  from  the  surface  of 
any  object  it  abstracts  heat  from  that  object;  and  when  perspiration  evapo- 
rates from  the  skin  it  carries  off  heat  and  cools  the  body.  In  health,  the  sweat 


HYGIENE  OF  THE  SKIN.  275 

well  wash  their  hair  every  day,  as  it  takes  so  long  to  dry; 
but  there  is  no  reason  why  a  man  should  not  immerse  his 
head  when  he  takes  his  bath.  Except  on  parts  of  the  skin 
especially  exposed  to  contamination,  soap  should  only  be 
used  occasionally — say  once  or  twice  a  week;  its  employ- 
ment is  quite  unnecessary  for  cleanliness,  except  on  ex- 
posed parts  of  the  body,  if  frequent  bathing  is  a  habit  and  the 
skin  be  well  rubbed  afterwards  until  dry.  Soap  nearly  al- 
ways contains  an  excess  of  alkali,  which  in  itself  injures  some 
skins,  and,  besides,  is  apt  to  combine  chemically  with  the 
sebaceous  secretion  and  carry  it  too  freely  away.  Persons 
whose  skin  is  injured  by  soap,  will  find  in  cornmeal 
a  good  substitute.  No  doubt  many  folk  go  about  in  very 
good  health  with  very  little  washing;  contact  with  the 
clothes  and  other  external  objects  keeps  the  skin  excretions 
from  accumulating  to  any  very  great  extent.  But  apart  from 
the  duty  of  personal  cleanliness  imposed  on  every  one  as  a 
member  of  society  in  daily  intercourse  with  others,  the  mere 
fact  that  the  healthy  body  can  manage  to  get  along  under 
unfavorable  conditions  is  no  reason  for  exposing  it  to  them. 
A  clogged  skin  throws  more  work  on  the  lungs  and  kid- 
neys than  their  fair  share,  and  the  evil  consequences  may 
be  experienced  any  day  when  something  else  throws  an- 
other extra  strain  upon  them. 

Bathing. — One  object  of  bathing  is  to  cleanse  the  skin; 

How  often  should  soap  be  used  in  the  bath?  Why  is  the  too  fre- 
quent use  of  soap  not  desirable?  What  is  a  good  substitute  for  it  in 
cases  where  soap  is  injurious  to  the  skin?  How  does  an  unclean  skin 
influence  internal  organs?  When  are  its  results  apt  to  show  them- 
selves? 

glands  secrete  more  vigorously  when  the  body  is  heated,  and  so  cool  it  and  keep 
down  its  temperature.  In  most  fevers  the  sweat  glands  are  paralyzed;  and  the 
abnormally  warm  body  is  not  cooled  by  loss  of  the  heat,  which  in  health  would 
have  been  carried  off  by  the  evaporating  sweat. 


276  THE  HUMAN  BODY. 

but  it  is  also  useful  to  strengthen  and  invigorate  the  whole 
frame.  For  strong  healthy  persons  a  cold  bath  is  the  best;  in 
severe  weather  the  temperature  of  the  water  should  be  raised 
to  15°  0.  (about  60°  F.),  at  which  it  still  feels  quite  cool  to 
the  surface.  The  first  effect  of  a  cold  bath  is  to  contract  all 
the  skin-vessels  and  make  the  surface  pallid.  This  is  soon 
followed  by  a  reaction,  in  which  the  skin  becomes  red  and 
full  of  blood,  and  a  glow  of  warmth  is  felt  in  it.  The 
proper  time  to  come  out  of  the  bath  is  while  this  reaction 
lasts,  and  after  emersion  it  should  be  promoted  by  a  good 
rub.  If  the  stay  in  the  cold  water  be  too  prolonged  the 
state  of  reaction  passes  off,  the  skin  again  becomes  pallid, 
and  the  person  probably  feels  cold,  uncomfortable,  and  de- 
pressed all  day:  then  bathing  is  injurious  instead  of  bene- 
ficial; it  lowers  instead  of  stimulating  the  activities  of  the 
body.  How  long  one  may  remain  in  cold  water  with  benefit, 
depends  greatly  on  the  individual;  a  vigorous  man  can  bear 
and  set  up  a  healthy  reaction  after  much  longer  immer- 
sion than  a  feeble  one;  moreover,  a  person  used  to  cold 
bathing  can  with  benefit  remain  in  the  water  longer  than 
one  not  accustomed  to  it.  Of  course,  apart  from  this,  the 
temperature  of  the  water  has  a  great  importance.  Water 
which  feels  cold  to  the  skin  may,  as  shown  by  the  ther- 
mometer, vary  within  very  wide  limits  of  temperature.  The 
colder  it  is,  the  shorter  the  time  which  it  is  wise  to  remain 
in  it. 

When  to  Bathe. — It  is  perfectly  safe  to  bathe  when  warm, 

What  ends  are  obtained  by  bathing?  What  sort  of  a  bath  should 
healthy  persons  take?  What  is  the  primary  effect  of  a  cold  bath  on 
a  healthy  person?  What  follows  next?  When  should  one  leave 
a  cold  bath?  What  happens  if  one  stays  too  long  in  a  cold  bath? 
Point  out  conditions  which  influence  the  time  of  remaining  with 
benefit  in  a  cold  bath. 


SHOWER  BATHS  AND   WARM  BATHS.  277 

provided  the  skin  is  not  perspiring  profusely;  the  common 
belief  to  the  contrary  notwithstanding.  On  the  other  hand, 
no  one  should  enter  a  cold  bath  when  feeling  chilly,  or  in 
a  depressed  vital  condition.  It  is  not  wise  to  take  a  cold 
bath  immediately  after  a  meal,  for  the  afterglow  of  the  skin 
tends  to  draw  away  too  much  blood  from  the  digestive 
organs,  which  are  then  actively  at  work.  The  best  time  for 
a  long  bath  is  two  or  three  hours  after  breakfast;  but  for  a 
brief  daily  dip  there  is  no  better  time  than  while  the  body 
is  still  warm  from  bed. 

Shower  Baths  abstract  less  heat  from  the  body  than  an 
ordinary  cold  bath,  and  at  the  same  time  give  it  a  greater 
stimulus,  tending  to  set  up  the  worm  reaction.  Hence  they 
are  valuable  to  persons  in  not  very  vigorous  health. 

Warm  Baths,  except  occasionally  for  purposes  of  clean- 
liness, are  medical  remedies,  and  not  proper  things  for 
daily  use.  While  promoting  the  tendency  to  perspiration 
(which  it  is  often  important  to  do  in  disease),  they  also, 
if  often  repeated,  lower  the  general  vigor  of  the  body. 
Persons  in  feeble  health,  who  cannot  stand  an  ordinary 
daily  cold  bath,  may  diminish  the  shock  to  the  system  by 
raising  the  temperature  of  the  water  they  bathe  in  to  any 
point  at  which  it  still  feels  cool  to  the  skin. 

Is  it  ever  safe  to  bathe  while  warm?  Point  out  conditions  when 
a  cold  bath  should  be  avoided.  Why  is  it  not  wise  to  take  a  cool 
bath  soon  after  a  meal?  Wliat  is  the  best  time  for  a  prolonged  cold 
bath?  What  the  best  time  for  a  brief  daily  dip? 

Why  are  shower  baths  better  than  immersion  baths  for  persons  in 
enfeebled  health? 

Should  healthy  persons  take  daily  warmbaths?  What  is  the  con- 
sequence of  frequent  warm  baths? 

How  should  persons  iii  feeble  health  regulate  the  temperature  of 
their  daily  bath? 


278  THE  HUMAN  BODY. 


APPENDIX  TO   CHAPTER  XVIII. 

To  demonstrate  the  anatomy  of  the    renal  organs  proceed  as 
follows: 

1.  Kill  a  rat  in  any  merciful  way;  placing  it  under  a  bell-jar 
with  a  sponge  soaked  in  ether  is  a  good  method. 

2.  Open  the  abdomen  of  the  animal,  remove  its  alimentary  canal, 
and  cut  away  (with  stout  scissors)  the  ventral  portion  of  the  pelvic 
girdle.     The  dark-red  kidneys  will  then  be  easily  recognized  on  each 
side  of  the  dorsal  part  of  the  abdominal  cavity,  the  right  one  nearer 
the  head  than  the  left. 

3.  Dissect  away  neatly  the  connective  tissue,  etc.,  in  front  of  the 
vertebral  column,  so  as  to  clean  the  inferior  vena  cava  and  the  abdom- 
inal aorta.     Trace  out  the  renal  arteries  and  veins. 

4.  Find  the  ureter,  a  slender  tube  passing  back  from  the  kidney 
towards  the  pelvis:  it  leaves  the  inner  border  of  the  kidney  behind 
the  vein  and  artery;  and  lying,  at  first,  at  some  distance  from  the 
middle  line,  converges  towards  its  fellow  as  it  passes  back. 

5.  Follow  the  ureters  back  until  they  reach  the  urinary  bladder; 
dissect  away  the  tissues  around  the  latter  and  note  its  form,  etc. 

6.  Open  the  bladder;  find  the  apertures  of  entry  of  the  ureters, 
and  pass  bristles  through  them  into  those  tubes.     Note  the  mucous 
membrane  lining  the  bladder. 

7.  Remove  one  kidney  from  the  body  and  divide  it  from  its  outer 
to  near  its  inner  border;  turn  the  two  halves  apart  (still  leaving  them 
connected  by  the  tissues  at  the  inner  border),  and  examine  the  cut 
surfaces. 

8.  Note  at  the  inner  border  (fiilas)  the  dilatation  (pelvis)  of  the 
ureter;  the  outer,  darker,  granular  cortical  portion  of  the  kidney,  and 
the  inner,  paler,  smoother  medullary  portion;  the  papilla,  formed  by 
•i    projection  of  the  medullary  substance  at  the  hilus,  contained  in 
an  expansion  (calyx)  of  the  pelvis  of  the  ureter. 

9.  Obtain  a  fresh  sheep's  kidney.     Divide  it  by  a  section  made 
through  it  from  its  outer  to  its  inner  border.     On  the  cut  surfaces  the 
cortex  and  medulla  will  be  more  readily  demonstrated  than  on  the 
rat's  kidney.     The  pyramids  of  Malpighi  will  also  be  easily  seen,  and 
the  offshoots  of  the  cortex  extending  between  them. 


CHAPTER  XIX. 
WHY  WE  NEED  A  NERVOUS  SYSTEM.     ITS  ANATOMY. 

The  Harmonious  Co-operation  of  the  Organs  of  the 
Body. — We  have  already  learned  that  the  body  consists  of 
a  vast  number  of  cells  and  fibres,  combined  to  form  organs^ 
and  that  each  kind  of  cell  or  fibre  and  each  organ  has  its 
own  peculiar  structure,  properties,  and  uses.  Except  in  so 
far  as  the  blood,  passing  from  organ  to  organ,  carries  mat- 
ters from  one  to  another,  and  indirectly  enables  each  organ 
to  act  upon  the  rest,  we  have  as  yet  seen  no  means  by  which 
all  this  collection  of  organs  is  made  to  work  together,  so 
that  each  shall  not  merely  look  after  itself,  but  regulate  its 
activity  in  relation  to  the  needs  or  dangers  of  other  parts 
of  the  body. 

That  the  organs  do  co-operate  we  all  know.  The  lids 
shut  when  an  object  threatens  to  touch  the  eye,  and  (with- 
out our  thinking  about  it  at  all)  thrust  themselves  in  the 
way  so  as  to  protect  the  more  tender  eyuball.  When  we  are 
using  the  muscles  of  the  legs  vigorously  the  muscles  of 
respiration  hurry  their  action,  and,  consequently,  oxygen  is 
conveyed  more  rapidly  to  the  blood  for  the  supply  of  the 
working  leg  muscles,  and  the  carbon  dioxide  produced  in 
great  quantity  by  these  muscles  is  quickly  removed.  When 
the  sole  of  the  foot  is  tickled  the  muscles  of  the  thigh  and 

Of  what  is  the  body  made  up?  How  do  the  various  kinds  x>f 
cells,  fibres,  and  organs  differ?  How  does  the  blood  enable  each  organ 
to  influence  the  rest? 

Give  an  example  showing  the  co-operation  of  the  organs  of  the 
body.  Give  another  example.  A  third. 


280  THE  I1UHAN  BODY. 

leg,  which  are  not  directly  interfered  with  at  all,  contract 
and  jerk  the  foot  away  from  its  tormentor.  Everywhere 
we  find  this  co-operation  among  the  organs ;  and  it  is  only 
by  such  co-operation  that  our  oodies  are  able  to  continue 
alive.  In  ^Esop's  fable  we  are  told  how  the  arms  and  jaws 
declined  to  work  any  longer  in  providing  and  grinding  food 
for  the  lazy  stomach,  and  how  they  soon  came  to  grief  in 
consequence.  We  might  extend  the  fable,  and  go  on  to 
state  how  afterwards  the  stomach  made  up  its  mind  to 
digest  and  absorb  just  as  much  food  as  it  wanted  for  itself, 
and  not  bother  about  supplying  those  cantankerous  arms 
and  jaws,  and  the  moral  would  be  the  same:  if  the  stomach 
ceased  to  work  for  the  other  parts  they  soon  would  cease  to 
be  able  to  send  food  to  it,  and  so  it  would  itself  starve  in  turn. 
How  a  Man  differs  from  a  Collection  of  Living  Organs. 
— Throughout  the  body,  heart,  lungs,  stomach,  intestines, 
liver,  muscles,  and  skin,  all  need  one  another's  aid  to 
obtain  food  and  oxygen,  to  remove  wastes,  and  to  avoid  dan- 
gers. This  co-operation  makes  the  individual  human  be- 
ing ;  a  mere  mass  of  living  organs,  arranged  together  in  the. 
form  of  man's  body,  but  each  acting  without  reference  to 
the  rest,  would  no  more  make  a  man  than  a  mob  of  strong 
men  would  make  an  army.  As  in  the  mob  the  reckless 
courage  of  some,  the  personal  cowardice  of  others,  the 
uncontrolled  ambition  of  a  few,  would  make  the  crowd 
nearly  useless  for  military  purposes  in  spite  of  the  merits  of 
its  individual  members,  so  in  the  body ;  if  the  organs  were 

Is  co-operation  between  its  organs  general  throughout  the  body? 
Is  it  important?  Illustrate  the  importance  of  co-operation  between 
the  parts  of  the  body. 

For  what  purposes  do  the  different  organs  need  one  another's  help? 
Is  the  co-operation  of  organs  necessary  to  make  a,n  individual  human. 
Illustrate, 


CO-ORDINATION.  281 

not  disciplined,  controlled,  and  guided,  so  as  to  work  to- 
gether for  the  good  of  the  whole,  death  would  very  soon 
result.  As  a  matter  of  fact  this  is  the  way  in  which  death 
almost  always  does  begin.  The  body  is  not  built  like  the 
deacon's  "one-boss  shay/'  to  run  till  every  part  of  it  gives 
out  at  the  same  moment.  Some  important  organ  ceases  to 
do  its  part  properly;  as  a  consequence  the  whole  complex 
mechanism  is  thrown  out  of  gear,  and  deatn  results. 

Co-ordination  means  controlling  the  activities  of  a  num- 
ber of  working  things  (whether  men,  or  organs,  or  ma- 
chines) for  the  attainment  of  a  definite  end.  A  pro- 
miscuous and  undirected  crowd  of  competent  bricklayers, 
carpenters,  hod-carriers,  and  so  forth,  would  be  quite  in- 
competent to  build  a  house.  There  might  be  present 
abundant  energy  and  skill  to  construct  walls  and  floors  and 
roof;  but  if  each  man  worked  for  himself  and  took  no  heed 
of  the  rest  the  result  would  be  an  odd  building,  if  any  at 
all.  Hence  the  whole  work  is  placed  under  the  control  of 
a  master  builder,  who  guides  the  activities  of  individ- 
uals according  to  the  needs  of  the  moment:  undirected 
workmen,  if  conscientious,  would  work  jufct  as  hard  with- 
out supervision,  but  they  would  work  unni 
healthy  body  may  be  regarded  as  made  up  <j  imber  of 

conscientious  workers,  the  organs,  who  aiv  ;ed  in 

building  it  and  keeping  it  in  repair,  each  one  acting  so  as 
to  co-operate  with  the  rest  for  the  attainir 
mon  end.     The  master  builder,  or  "boss,"  if  we  may  use 


How  does  death  usually  begin?    What  happens  v  h<>-u  spme  im- 
portant organ  ceases  to  do  its  duty? 

What  is  meant   by   co-ordination?     Illustrate.      How  mny  the 
healthy  body  be  regarded  when  compared  with  t\ie  worknu 
qerned  in  building  a  house? 


! 


282  THE  HUMAN  BODY. 

such  a  word,  i^  ..-epresented  by  the  nervous  system,  which 
is  in  communication  with  all  the  other  organs,  is  influenced 
by  the  condition  and  the  needs  of  every  part  at  each  mo- 
ment, and  guides  the  activity  of  all  the  others  accordingly. 
Part  of  this  control  is  exercised  consciously  and  with  the 
co-operation  of  the  "will,"  but  much  more  is  carried  on  by 
the  nervous  system  without  our  knowing  anything  about  it. 
Nerve-Trunks  and  Nerve-Centres. — In  dissecting  the 
body  numerous  white  cords  are  found  which  at  first  sight 
might  be  taken  for  tendons.  That  they  are  something  else 
soon  becomes  clear,  since  a  great  many  of  them  have  no 
connection  with  muscles,  and  those  which  have,  usually 
enter  near  the  middle  of  the  belly  of  the  muscle,  instead  of 
being  fixed  to  its  ends  as  most  tendons  are.  These  cords 
are  nerve-trunks :  followed  from  the  middle  line  of  the 
body  each  (Fig.  79)  will  be  found  to  break  up  into  finer 
and  finer  branches,  until  the  subdivisions  become  too  small 
to  be  followed  without  the  aid  of  a  microscope.  Traced 
towards  the  middle  of  the  body  the  trunk  will,  in  most 
cases,  be  found  to  increase  by  the  union  of  others  with  it, 
and  ultimately  to  join  a  much  larger  mass  of  different 
structure,  from  which  other  similar  trunks  spring.  This 
mass  is  nerve-centre.  The  end  of  a  nerve  attached  to  the 
centre  is,  naturally,  its  central,  and  the  other  its  distal  or 
peripheral  end. 

What  is  it  in  the  body  which  represents  the  master  builder? 
What  are  the  relations  between  the  nervous  system  and  the  other 
organs  of  the  body  ?  Is  the  control  of  the  nervous  system  always  con- 

ly  exercised? 

How  n.ay  we  recognize  that  certain  white  cords  found  on  dissect- 

•T  the  be  ly  -in   not  tendons?    What  are  they?    What  is  found  when 

•iced  towards  the  outer  parts  of  the  body?     What 

a  traced  m   the   opposite  direction?     What  is   a  nerve-centre? 

.1  by    lie  peripheral  end  of  a  nerve? 


DIAGRAM  OF  THE  NERVOUS  SYSTEM. 


283 


FIG.  r9.-Diagram  illustrating  the  general 


arrangement  of  the  nervous 


284*  THE  HUMAN  BODY. 

Nerve-centres  give  origin  to  nerve-trunks  ;  these  radiate 
all  over  the  body,  branching  and  becoming  smaller  and 
smaller  as  they  proceed  from  the  centre  ;  finally  they  end 
in  or  among  the  cells  and  fibres  of  the  various  organs. 
The  general  arrangement  of  the  nerve-centres  and  of  the 
larger  nerve-trunks  of  the  body  is  shown  in  Fig.  79. 

The  Main  Nerve-Centres. — The  great  majority  of  the 
nerve-trunks  take  their  origin  from  the  brain  and  spinal 
cord)  which  together  form  the  great  cerebro-spinal  centre. 
Some  nerves,  however,  commence  in  rounded  or  oval 
masses,  which  vary  in  size  from  that  of  the  kernel  of  an 
almond  down  to  microscopic  dimensions,  and  which  are 
widely  distributed  in  the  body.  Each  of  these  smaller 
centres  is  called  a  ganglion.  A  considerable  number  of  the 
largest  ganglia  are  united  directly  to  one  another  by  nerve- 
trunks,  and  give  off  nerves  especially  to  blood-vessels  and 
to  the  organs  in  the  thoracic  and  abdominal  cavities.  These 
ganglia  and  their  branches  form  the  sympathetic  nervous 
system  (Figs.  1  and  2),  as  distinguished  from  the  cerebro- 
spinal  nervous  system,  consisting  of  the  brain  and  spinal 
cord  and  the  nerves  proceeding  from  and  to  them. 

The  Cerebro-Spinal  Centre  and  its  Membranes. — Lying 
in  the  skull  is  the  brain,  and  in  the  neural  canal  of  the 
vertebral  column  the  spinal  cord  or  spinal  marrow, 
the  two  being  continuous  through  the  foramen  magnum 


To  what  do  nerve-centres  give  origin?  What  becomes  of  nerve- 
trunks? 

From  what  organs  do  most  nerves  arise?  What  is  meant  by  the 
cerebro- spinal  centre?  From  what  do  those  nerves  arise  which  are 
not  directly  connected  with  brain  and  spinal  cord?  What  are  the 
smaller  nerve-centres  named?  What  is  the  sympathetic  nervous  sys, 
tern?  Where  is  the  brain  placed?  What  organ  lies  in  the  neural  canal 
of  the  backbone?  Through  what  opening  do  brain  and  spinal  cord 
unite? 


THE  CEREBRO-SPINAL   CENTRE. 


285 


(Fig.  20)  of  the  occipital  bone. 
This  cerebro-spinal  centre  con- 
sists of  similar  right  and  left 
halves,  incompletely  separated 
by  grooves  and  fissures.  Brain 
and  spinal  cord  are  very  soft 
and  easily  crushed  ;  accordingly, 
both  are  placed  in  almost  com- 
pletely closed  bony  cavities,  and 
are  also  enveloped  by  mem- 
branes which  give  them  sup- 
port. These  membranes  are 
three  in  number.  Externally 
is  the  dura  mater,  tough  and 
strong,  and  composed  of  con- 
nective tissue.  The  innermost 
enveloping  membrane  of  the 
cerebro-spinal  centre,  in  imme- 
diate contact  with  the  proper 
nervous  parts,  is.  the  pia  mater, 
less  dense  and  tough  than  the 
dura  mater.  Covering  the  out- 
side of  the  pia  mater  is  a  layer  of 
flat  cells  ;  a  similar  layer  lines 
the  inside  of  the  dura  mater, 
and  these  two  layers  are  de- 
scribed as  the  third  membrane 


•d 

9,* 


Why  are  brain  and  spinal  cord 
placed  in  bony  chambers?  How 
many  membranes  also  support  them? 
What  is  the  outside  membrane 
named?  What  are  its  mechanical 
properties?  Of  what  is  it  composed? 
Wuut  is  the  pia  mater? 


286 


THE  HUMAN  BODY. 


of  the  cerebro-spinal  centre,  called  the  arachnoid.  In  the 
space  between  the  two  layers  of  the  arachnoid  is  a  small 
quantity  of  watery  cerebro-spinal  liquid. 

The  Spinal  Cord  (Fig.  80)  is  nearly  cylindrical  in  form, 
being,  however,  a  little  wider  from  side  to  side  than  dorso- 
ventrally,  and  tapering  off  at  its  posterior  end.  Its  aver- 
age diameter  is  about  j  inch  and  its  length  17  inches. 
It  weighs  1-J-  ounces.  There  is  no  marked  limit  be- 


Fio.  81.— The  spinal  cord  and  nerve-roots.  A,  a  small  portion  of  the  cord 
seen  from  the  ventral  side;  B,  the  same  seen  laterally;  C,  a  cross-section  of  the 
cord;  Z>,  the  two  roots  of  a  spinal  nerve;  1,  anterior  (ventral)  fissure;  2,  poste- 
rior (dorsal)  fissure  ;  3,  surface  groove  along  the  line  of  attachment  of  the 
anterior  nerve-roots;  4,  line  of  origin  of  the  posterior  roots;  5,  anterior  root 
filaments  of  a  spinal  nerve;  6,  posterior  root  filaments;  6',  ganglion  of  the  pos- 
terior root ;  7,  7'.  the  first  two  divisions  of  the  nerve-trunk  after  its  formation 
by  the  union  of  the  two  roots. 


What  is  Hie  arachnoid?    What  is  the  cerebro-spinal  liquid? 
What  is  the  general  form  of  the  spinal  cord?     Its  average  diame- 
ter?   Its  length?    Its  weight?    How  does  it  connect  with  the  brain? 


THE  SPINAL    CORD  AND   THE  SPINAL  NERVES.    287 

tween  the  spinal  cord  and  the  brain,  the  one  passing 
gradually  into  the  other.  In  its  course  the  cord  presents 
two  expansions,  an  upper,  10  (Fig.  80),  the  cervical  en- 
largement, reaching  from  the  third  cervical  to  the  first 
dorsal  vertebrae,  and  a  lower  or  lumbar  enlargement)  9, 
opposite  the  last  dorsal  vertebras. 

Running  along  the  middle  line  on  both  the  ventral  and 
the  dorsal  aspects  of  the  cord  are  fissures  which  (C,  Fig. 
81)  nearly  divide  it  into  right  and  left  halves. 

A  transverse  section,  C,  shows  that  the  substance  of  the 
cord  is  not  alike  throughout,  but  that  its  white  superficial 
layers  envelop  a  central  gray  substance  arranged  somewhat 
in  the  form  of  a  capital  H.  Each  half  of  the  gray  matter 
is  crescent-shaped,  and  the,  crescents  are  turned  back  to 
back  and  united  across  the  middle  line  by  the  gray  com- 
missure. 

The  Spinal  Nerves. — Thirty-one  pairs  of  spinal  nerves 
join  the  spinal  cord  in  the  neural  canal  of  the  vertebral 
column,  entering  the  canal  through  the  inter  vertebral  fora- 
mina (p.  32).  Each  divides  in  the  foramen  into  a  dorsal 
and  ventral  portion,  known  respectively  as  the  posterior 
and  anterior  roots  of  the  nerve  (6  and  5,  Fig.  81),  and 
these  are  attached  to  the  sides  of  the  cord.  On  each  pos- 
terior root  is  a  spinal  ganglion  (6',  Fig.  81),  placed  where 


What  expansions  are  seen  in  it?     Where  is  each  placed? 

How  are  the  right  and  left  halves  of  the  cord  separated? 

Is  the  spinal  cord  alike  all  through?  What  are  the  colors  of  its 
outer  and  of  its  inner  portions?  What  is  the  form  of  the  gray  mat- 
ter of  the  cord  as  seen  on  cross-sections?  How  are  the  crescents 
united? 

How  many  spinal  nerves  are  there?  What  do  thoy  join?  How 
do  they  get  into  the  neural  canal?  Where  do  they  divide?  What 
are  the  divisions  named?  To  what  are  they  attached?  What  is 
found  on  each  posterior  root? 


288  THE  HUMAN  BODY. 

it  joins  the  anterior  root  to  make  up  the  common  nerve- 
trunk.  Immediately  after  its  formation  by  the  mixture  of 
fibres  from  both  roots,  the  trunk  begins  to  divide  into 
branches  for  the  supply  of  some  region  of  the  body. 

The  Brain  (Fig.  82)  is  far  larger  than  the  spinal  cord 
and  more  complex  in  structure.  It  weighs  on  the  average 
about  50  ounces  in  the  adult.  The  brain  consists  of  three 
main  masses,  each  with  subsidiary  parts,  following  one  an- 
other in  series  from  before  back,  and  respectively  known 
as  the  fore-brain,  mid-brain,  and  hind-brain.  In  man 
the  fore-brain,  A,  weighing  about  44  ounces,  is  much 
larger  than  all  the  rest  put  together  and  laps  over  them. 


FIG.  82.— Diagram  illustrating  the  general  relationships  of  the  parts  of  the 
brain.  A,  fore-brain;  6,  mid-brain;  B,  cerebellum;  C,  pons  Varolii ;  D,  medulla 
oblongata;  B,  C,  and  D  together  constitute  the  hind-brain. 

What  becomes  of  the  common  trunk  formed  by  the  mixture  of 
the  roots? 

Point  out  characters  in  which  the  brain  differs  from  the  spinal 
cord.  What  is  its  weight?  Of  what  main  divisions  is  the  brain 
composed?  Which  is  the  largest  division?  Its  weight? 


THE  FORE-BRAIN.  289 

It  is  chiefly  formed  of  two  large  convoluted  musses,  sepa- 
rated from  one  another  by  a  deep  fissure,  and  known  as 
the  cerebral  hemispheres.  The  great  size  of  these  is  very 
characteristic  of  the  human  brain.  Beneath  each  cere- 
bral hemisphere  is  an  olfactory  lobe  (/,  Fig.  84),  incon- 
spicuous in  man  but  often  larger  than  the  cerebral  hemi- 
spheres, as. in  most  fishes.  The  mid  brain,  #,  forms  a 
connecting  isthmus  between  the  two  other  divisions.  The 
hind-brain  consists  of  three  main  parts:  on  its  dorsal  side 
is  the  cerebellum,  B,  Fig.  82;  on  the  under  side  is  the 
pons  Varolii,  C,  Fig.  82;  and  behind  is  the  medulla  ob- 
longata,  D,  Fig.  82,  which  joins  the  spinal  cord. 

In  nature  the  main  divisions  of  the  brain  are  not  sepa- 


Cb\ 


FIG.  83.— The  brain  from  the  left  side.  Cb,  the  cerebral  hemispheres  forming 
the  main  bulk  of  the  fore-brain;  Cbl,  the  cerebellum;  Mo,  the  medulla  oblon- 
gata;  P,  the  pons  Varolii;  *,  the  fissure  of  Sylvius. 

By  what  is  the  fore-brain  chiefly  formed?  What  lies  below  the 
cerebral  hemispheres?  Are  the  olfactory  lobes  ever  larger  than  the 
cerebral  hemispheres?  What  does  the  mid-brain  form?  Name  the 
main  divisions  of  the  hind-brain?  State  their  relative  positions. 
What  part  of  the  brain  joins  the  spinal  cord? 


THE  HUMAN  BODY. 


rated  so  much  as  has  been  represented  in  the  diagram  for 
the  sake  of  clearness,  but  lie  close  together  as  represented 
in  Fig.  83;  and  the  mid-  brain  is  entirely  covered  in  on  its 
dorsal  side.  Nearly  everywhere  the  surface  of  the 
brain  is  folded,  the  folds,  known  as  the  convolutions) 
being  deeper  and  more  numerous  in  the  brain  of  man 
than  in  that  of  the  animals  nearest  allied  to  him  zoologi- 
cally. 

The  brain,  like  the  spinal  cord,  consists  of  gray  and 
white  nervous  matter,  but  somewhat  differently  arranged; 
for  while  the  brain,  like  the  cord,  contains  gray  nerve-mat- 
ter in  its  interior,  a  great  part  of  its  surface  is  also  covered 
with  it.  By  the  external  convolutions  of  the  cerebellum 
and  of  the  cerebral  hemispheres  the  surface  over  which  this 
gray  substance  is  spread  is  very  much  increased. 

The  Cranial  Nerves.  —  Twelve  pairs  of  nerves  leave  the 
skull  cavity  by  apertures  in  its  base;  they  are  known  as  the 
cranial  nerves.  Most  of  them  spring  from  the  under  side 
of  the  brain,  which  is  represented  in  Fig.  84.  The  first 
pair,  or  olfactory  nerves,  are  the  nerves  of  smell;  they  arise 
from  the  under  sides  of  the  olfactory  lobes,  /,  and  pass  out 
through  the  roof  of  the  nose.  The  second  pair,  or  optic 
nerves,  II,  are  the  nerves  of  sight;  they  spring  from  the 
mid-brain,  and,  under  the  name  of  the  optic  tracts,  run 
down  to  the  under  side  of  the  fore-brain,  where  they  unite 


Is  the  surface  of  most  of  the  brain  smooth?  What  are  the  folds 
called?  How  does  a  man's  brain  differ,  as  regards  its  convolutions, 
from  an  ape's? 

Of  what  does  the  brain  consist?  How  does  the  arrangement  of 
white  and  gray  matter  in  it  differ  from  that  of  the  spinal  cord?  How 
is  the  surface  on  which  the  gray  matter  is  spread  increased? 

How  many  cranial  nerves  are  there?  Where  do  most  of  them 
originate?  Name  the  first  pair.  Where  do  they  arise?  Where  do 
they  pass  out?  Name  the  second  pair.  What  are  the  optic  tracts? 


THE  CRANIAL  NERVES. 


291 


FIG.  84. — The  base  of  the  brain.  The  cerebral  hemispheres  are  seen  over- 
lapping all  the  rest.  /  olfactory  lobes;  //,  optic  tract  passing  to  the  optic 
commissure  from  which  the  optic  nerves  proceed;  ///.  the  third  nerve  or  motor 
oculi;  IV,  the  fourth  nerve  or  patheticus;  V,  the  fifth  nerve  or  trigeminalix; 
VI.  the  sixth  nerve  or  abducens;  VII,  the  seventh  or  facial  nerve  or  portio  dura; 
VIII,  the  auditory  nerve  or  portio  moll  is;  IX,  the  ninth  or  glosso-pharyngeal; 
X,  the  tenth  or  pneumogastric  or  vagus;  XI,  the  spinal  accessory;  XII,  the 
hypoglossal;  nc/,  the  first  cervical  spinal  nerve. 

to  form  the  optic  commissure,  from  which  an  optic  nerve 
proceeds  to  each  eyeball. 

All  the  remaining  cranial  nerves  arise  from  the  hind- 
brain.     The  third  pair,  III.,  (motores  oculi,  or  movers  of  the 

What  is  the  optic  commissure?    Where  does  each  optic  nerve  cro? 
How  many  pairs  of  cranial  nerves  arise  from  the  hind-brain? 
Name  the  third  pair.     What  is  their  distribution? 


292  THE  HUMAN  BODY. 


are  distributed  to  most  of  the  muscles  which  move 
the  eyeball  and  also  to  that  which  lifts  the  upper  eyelid. 

The  fourth  pair,  IV,  (pathetiei,)  are  quite  small;  each 
goes  to  one  muscle  of  the  eyeball. 

The  fifth  pair  of  cranial  nerves,  V,  (trigeminals,)  re- 
semble the  spinal  nerves  in  having  two  roots,  one  of  which 
possesses  a  ganglion  (the  Gasserian  ganglion}.  Beyond 
the  ganglion  the  two  roots  form  a  common  trunk  which 
divides  into  three  main  branches.  The  first  of  these,  the 
ophthalmic,  is  distributed  to  the  muscles  and  skin  over  the 
forehead  and  upper  eyelid;  and  also  gives  branches  to  the 
mucous  membrane  lining  the  nose,  and  to  the  integument 
over  that  organ.  The  second  division  (superior  maxillary 
nerve)  of  the  trigeminal  gives  branches  to  the  skin  over  the 
temple,  to  the  cheek  between  the  eyebrow  and  the  angle  of 
the  mouth,  and  to  the  upper  teeth;  as  well  as  to  the  mu- 
cous membrane  of  the  nose,  pharynx,  soft  palate  and  roof 
of  the  mouth.  The  third  division  (inferior  maxillary]  is 
the  largest  branch  of  the  trigeminal.  It  is  distributed  to 
the  side  of  the  head  and  the  external  ear,  the  lower  lip 
and  lower  part  of  the  face,  the  mucous  membrane  of  the 
mouth  and  the  anterior  two  thirds  of  the  tongue,  the  lower 
teeth,  the  salivary  glands,  and  the  muscles  which  move  the 
lower  jaw  in  mastication. 

The  sixth  pair  of  cranial  nerves,  VI,  (alducentes,}  are 
distributed  each  to  one  muscle  of  the  eyeball  on  its  own 
side. 

What  is  the  distribution  of  the  fourth  pair? 

Name  the  fifth  pair  of  cranial  nerves.  How  do  they  resemble  the 
spinal  nerves?  What  is  the  ganglion  on  one  root  called?  Into  how 
many  main  branches  does  the  common  trunk  divide?  Name  the  first 
branch.  State  its  distribution.  The  second  branch.  Its  distribu 
tion.  The  third  main  brunch.  Its  distribution. 

Name  the  sixth  pair  of  cranial  nerves.     Where  do  they  go? 


NERVOUS  SYSTEM.  293 

The  seventh  pair  (facial  nerves),  VII,  are  distributed  to 
Uiost  of  the  muscles  of  the  face  and  scalp. 

The  eighth  pair  (auditory  nerves),  VIII,  are  the  nerves 
of  hearing,  and  are  distributed  to  the  inner  part  of  the  ear. 

The  ninth  pair  of  cranial  nerves  (glosso-pharyngeal), 
IX,  are  distributed  chiefly  to  tongue  and  pharynx. 

The  tenth  pair  (pneumogastric  nerves  or  vagi),  X,  give 
branches  to  the  pharynx,  gullet  and  stomach,  the  larynx, 
windpipe  and  lungs,  and  to  the  heart.  The  vagi  run  far- 
ther through  the  body  than  any  other  cranial  nerves. 

The  eleventh  pair  (spinal  accessory  nerves),  XI,  do  not 
arise  mainly  from  the  brain,  but  from  the  spinal  cord  by  a 
number  of  roots  attached  to  its  upper  portion,  between  the 
anterior  and  posterior  roots  of  the  proper  spinal  nerves. 
Each  enters  the  skull  cavity  alongside  of  the  spinal  cord 
and,  getting  a  few  filaments  from  the  medulla  oblongata, 
passes  out  by  the  same  aperture  as  the  glosso-pharyngeal 
and  pneumogastric  nerves.  Outside  the  skull  the  spinal 
accessory  divides  into  two  branches,  one  of  which  joins  the 
pneumogastric  trunk,  while  the  other  is  distributed  to 
muscles  about  the  shoulders. 

The  twelfth  pair  of  cranial  nerves  (hypoglpssi),  XII,  are 
distributed  mainly  to  the  mtiscles  of  the  tongue. 

The  Sympathetic  Nervous  System. — The  ganglia  which 
form  the  main  centres  of  the  sympathetic  nervous  system 

Name  the  seventh  pair  of  cranial  nerves.  To  what  parts  are 
they  distributed? 

What  is  the  eighth  pair  called?  What  are  their  functions?  Where 
do  they  end  ? 

Name  the  ninth  pair.     State  their  distribution. 

Name  the  tenth  pair.     State  their  distribution. 

Name  the  eleventh  pair.  Where  do  they  arise?  How  do  they 
get  into  the  brain-case?  With  what  nerves  do  they  leave  the  brain- 
case?  State  their  distribution. 

Name  the  twelfth  pair  of  cranial  nerves.     State  their  distribution. 


294  THE  HUMAN  BODY. 

lie  in  two  rows  (s,  Fig.  1,  and  sy,  Fig,.  %),  one  on  each  side 
of  the  bodies  of  the  vertebrae.  Each  ganglion  is  united  by  a 
nerve-trunk  with  the  one  in  front  of  it  and  the  one  behind  it, 
and  so  two  chains  are  formed  reaching  from  the  base  of  the 
skull  to  the  coccyx.  In  the  trunk  region  these  chains  lie  in  the 
ventral  cavity,  their  relative  position  in  which  is  indicated 
by  the  dots  sy  in  the  diagrammatic  transverse  section  repre- 
sented on  p,_9  in  Fig.  2. 

Each  sympathetic  ganglion  is  united  by  branches  to 
neighboring  spinal  nerves,  and  near  the  skull  to  various 
cranial  nerves  also;  from  the  ganglia  and  their  uniting  corda 
arise  numerous  trunks,  which  in  the  thorax  and  abdomen 
form  networks,  from  which  nerves  are  given  off  to  the  or- 
gans situated  in  those  cavities.  Many  sympathetic  nerves 
finally  end  in  the  walls  of  the  blood-vessels  of  various  or- 
gans. To  the  naked  eye  they  are  commonly  grayer  in  color 
than  the  cerebro-spinal  nerves. 

By  means  of  the  junctions  between  the  cranial  and  spinal 
nerves  and  the  sympathetic  system  the  brain  is  enabled  to 
control  the  parts  supplied  by  the  sympathetic  system. 

The  Three  Kinds  of  Nerve  Tissue. — The  microscope 
shows  that.ihe  nervous  organs  contain  tissues  peculiar  to 
themselves,  known  as  nerve-fibres  and  nerve-cells.  The 


How  are  the  ganglia  of  the  sympathetic  system  arranged? 

How  is  each  united  to  others?  How  far  through  the  body  d<r 
the  chains  of  sympathetic  ganglia  extend?  Where  are  the.  sym- 
pathetic chains  situated  in  the  trunk  of  the  body? 

How  are  the  sympathetic  ganglia  united  with  spinal  and  cranial 
nerves?  What  arise  from  the  ganglia?  What  do  they  form  in  the 
trunk  region  of  the  body?  Where  do  many  sympathetic  nerve- 
fibres  end?  How  do  sympathetic  nerves  differ  to  the  unaided  eye 
from  spinal  or  cerebral  nerves?  How  is  the  braiii  enabled  to  control 
the  parts  supplied  by  the  sympathetic  system? 

How  many  kinds  of  nerve-tissue  are  iliere?  What  are  the  pecul- 
iar nerve-tissues  called? 


NERVE-FIBRES. 


295 


cells  are  found  in  the  centres  only;  while  the  fibres,  of 
which  there  are  two  main  varieties  known  as  the  white  and 
the  gray,  are  found  in  both  trunks  and  centres;  the  white 
variety  predominating  in  the  cerebro  spinal  nerves  and  in 
the  white  substance  of  the  centres,  and  the  gray  in  the  sym- 
pathetic trunks  and  the  gray  portions  of  the  central  organs. 
White  Nerve-Fibres  consist  of  extremely  delicate  threads, 
about  ^Vir  inch  in  diameter,  but  frequently  of  a  length 


23  2 

\  !  / 


FIG.  85. 


. 

Z   3 
FIG.  86. 


FIG.  85.— White  nerve-fibres  soon  after  removal  from  the  body  and  when  they 
have  acquired  their  double  contour. 

FIG.  06. — Diagram  illustrating  the  structure  of  a  white  or  medullated  nerve- 
fibre.  1,  1,  primitive  sheath;  2,  2,  medullary  sheath;  3,  axis  cylinder. 


Where  only  do  we  find  nerve-cells?  Where  are  nerve-fibres 
found?  How  many  main  kinds  of  nerve-fibres  are  there?  Name 
them.  Where  do  the  white  nerve-fibres  predominate?  Where  the 


gray 


escribe  white  nerve-fibres. 


296  THE  HUMAN  BODY. 

which  is  in  proportion  very  great.  Each  is  continuous 
from  a  nerve-centre  to  the  region  in  which  it  ends,  so 
that  the  fibres,  e.g.,  which  pass  out  from  the  spinal  cord 
and  run  on  to  the  skin  of  the  toes,  are  three  to  four 
feet  long.  If  a  perfectly  fresh  white  nerve-fibre  be  exam- 
ined with  the  microscope  it  presents  the  appearance  of  a 
homogeneous  glassy  thread;  but  soon  it  acquires  a  charac- 
teristic double  border  (Fig.  85)  from  the  coagulation  of  a 
.portion  of  its  substance,  as  a  result  of  which  three  layers 
are  brought  into  view.  Outside  is  a  thin  transparent  en- 
velope (1,  Fig.  86)  called  the  primitive  sheath;  inside  this 
is  a  fatty  substance,  2,  forming  the  medullary  sheath  (the 
coagulation  of  which  gives  the  fibre  its  double  border),  and 
in  the  centre  is  a  core,  the  axis  cylinder,  3,  which  is  the  es- 
sential part  of  the  fibre,  since  near  its  ending  the  primitive 
and  medullary  sheaths  are  frequently  absent.  At  intervals 
of  about  ^  inch  along  the  fibre  are  found  nuclei.  These 
are  indications  of  the  primitive  cells  which  by  their  elon- 
gation, fusion,  and  other  modifications  have  built  up  the 
nerve-fibre.  In  the  course  of  a  nerve-trunk  its  fibres  rarely 
divide;  when  a  branch  is  given  off  some  fibres  merely  sepa- 
rate from  the  rest,  much  as  a  skein  of  silk  might  be  sepa- 
rated at  one  end  into  smaller  bundles  containing  fewer 
threads. 

Gray  Nerve-Fibres  have  no  medullary  sheath,  and  con- 
sist merely  of  an  axis  cylinder  and  primitive  sheath.  Gray 

Is  each  nerve-fibre  continuous  from  centre  to  end?  Point  out 
nerve-fibres  three  or  four  feet  long.  What  is  the  appearance  under 
the  microscope  of  a  quite  fresh  white  nerve-fibre?  How  does  it  soon 
alter?  Name  the  layers  then  seen  and  state  their  relative  positions. 
Which  is  the  essential  part  of  the  nerve-fibre?  Give  a  reason  for 
your  statement.  What  are  found  at  intervals  along  the  nerve-fibre? 
What  do  they  indicate? 

What  occurs  when  a  nerve-trunk  branches? 


NERVE-CELLS. 


297 


fibres  are  especially  abundant  in  the  sympathetic  trunks; 
and  they  alone  are  found  in  the  olfactory  nerve. 

Nerve-Cells. — As  far  as  our  knowledge  at  present  goes, 
all  nerve -fibres  begin  as  branches  of  nerve-cells. 


FIG.  87.— Different  forms  of  nerve-cells  from  the  spinal  cord.  1,  a  cell  from 
the  anterior  part  of  the  gray  matter,  and  believed  to  be  connected  with  a  motor 
nerve-fibre;  2.  a  cell  from.the  posterior  part  of  the  gray  matter,  believed  to  be 
connected  with  sensory  fibres. 

At  1,  Fig.  87,  is  shown  a  nerve-cell  such  as  may  be 
found  in  the  anterior  part  of  the  gray  matter  of  the  spinal 
cord.  It  consists  of  the  cell  body,  or  cell  protoplasm,,  con- 
taining a  large  nucleus,  in  which  is  a  nucleolus.  From  the 

Describe  a  gray  nerve-fibre.  Where  are  they  especially  numerous  ? 
Name  a  cranial  nerve  that  consists  entirely  of  them. 
How  do  nerve-fibres  begin  ? 
Of  what  does  a  nerve-cell  consist  ? 


298  THE  HUMAN  BODY. 

body  of  the  cell  arise  several  branches  the  great  majority 
of  which  rapidly  subdivide.  One  process  of  the  cell  («), 
although  giving  off  several  very  fine  branches,  retains  its 
individuality,  and  is  continued  as  the  axis  cylinder  of  a 
nerve-fibre  in  an  anterior  spinal  root.  At  2,  in  Fig.  87,  is 
represented  a  nerve- cell  from  the  posterior  part  of  the  gray 
matter  of  the  spinal  cord.  It  also  has  an  axis-cylinder 
process,  differing  somewhat  in  its  way  of  branching  from  1, 
but  probably  ultimately  giving  rise  to  one  or  more  cylinder- 
axes  of  sensory  nerve-fibres.  Cells  such  as  those  represented 
in  Fig.  87  are  found  also  in  many  parts  of  the  brain. 

The  Structure  of  Nerve-Centres — These  consist  of  white 
and  gray  nerve-fibres,  of  nerve-cells,  and  of  connective  tis- 
sue and  blood-vessels,  arranged  together  in  different  ways 
in  the  different  centres. 

What  arise  from  the  protoplasm  of  a  nerve-cell?  What  becomes 
of  most  of  the  branches?  How  does  one  branch  of  some  nerve- 
cells  of  the  spinal  cord  differ  from  the  remainder?  As  regards  this 
branch,  how  do  other  nerve-cells  differ  from  the  above? 

Of  what  do  nerve-centres  consist? 


APPENDIX  TO  CHAPTER  XIX. 

1.  The  co-operation  of  the  parts  of  the  body  may  be  illustrated  as 
follows: 

a.  Feign  a  blow  at  a  person's  eye;  the  lids  will  close  involuntarily, 
even  if  he  be  told  beforehand  that  he  is  not  to  be  actually  struck. 

b.  Count  a  boy's  pulse  and  breathing  while  he  is  sitting  quietly, 
then   let  him  run  a  hundred  yards  at  full  speed,  and  immediately 
afterwards  again  count  pulse  and  breathing  movements.     Both  will 
be  found  accelerated;  the  breathing,  to  carry  off  from  the  blood  the 
carbon  dioxide  given  it  by  the  working  muscles,  and  to  bring  in  new 
oxygen  to  replace  the  large  amount  used  by  the  working  muscles; 
the  heart-beat,  to  renew  more  rapidly  the  blood-flow  through  the 
muscles. 

c.  Tickle  the  inside  of  the  nose  with  a  feather.     This,  in  itself. 


APPENDIX.     CHAPTER  XIX.  299 

does  not  interfere  with  the  breathing  muscles;  but  their  action  will 
be  almost  at  once  so  changed  as  to  produce  a  sneeze,  tending  to  clear 
and  protect  the  nose. 

2.  Kill  a  frog  with  ether  (note,  p.  68);  open  its  abdomen  and  re- 
move the  viscera.  At  the  back  of  the  abdominal  cavity  will  be  seen 
a  bundle  of  white  cords  (nerve-trunks)  passing  back  to  each  leg. 
They  soon  unite  into  one  mam  stem  (the  sciatic  nerve),  which  may 
be  easily  dissected  along  its  course  until  it  ends  in  fine  branches  in 
the  hind  limb. 

"3.  Kill  a  frog  and  expose  the  origin  of  the  sciatic  nerve  as  above. 
With  stout  scissors  then  cut  away  bit  by  bit,  and  very  carefully,  the 
bodies  of  the  vertebrae  (which  will  be  seen  projecting  in  the  middle 
line  at  the  back  of  the  abdominal  cavity)  until  the  neural  canal  is 
laid  open  and  the  spinal  cord  exposed.  You  will  probably  fail  the 
first  time,  but  on  the  second  attempt  succeed  in  doing  this  without 
cutting  the  nerve  trunks  as  they  pass  between  the  vertebrae  to  join 
the  spinal  cord.  On  the  specimen  thus  prepared  the  origin  of  the 
nerves  from  the  spinal  cord,  and  their  division  into  anterior  and  pos- 
terior (ventral  and  dorsal)  roots  before  they  join  the  cord  can  be 
demonstrated,  also  the  ganglionic  enlargements  on  the  posterior 
roots. 

4.  The  general  form,  the  cervical  and  lumbar  enlargements,  etc., 
of  the  spinal  cord  may  be  shown  on  a  frog.     Having  killed  the  ani- 
mal, remove  the  skin  and  muscles  on  the  dorsal  side  of  the  spinal 
column.     With  great  care  cut   away  the  upper  two  thirds  of   the 
neural  arches  of  the  vertebne.     Then  remove  the  upper  half  of  the 
skull  cavity.     Gently  raising  piece  by  piece  the  exposed   brain  and 
spinal  cord,  divide  the  nerves  which  spring  from  them  and  lift  out 
the  whole  cerebro-spinal  centre  and  place  it  in  alcohol  for  twenty- 
four  hours.     Demonstrate  the  origin  of  nerves  from  both  brain  and 
cord,  the  union  of  the  brain  and  cord,  etc.  etc.     The  specimen  may 
be  preserved  in  alcohol  for  future  use. 

5.  A  frog's  brain  differs  in  many  important  points  from  that  of 
man,  as  in  the  very  small  cerebellum,  the  comparatively  small  cere- 
bral hemispheres,  the    comparatively  large   mid-brain  and   the  ab- 
sence of  convolutions.     To  demonstrate  the  main   anatomical  fea- 
tures of  the  brain  that  of  a  mammal  is  necessary. 

a.  Obtain  a  fresh  calf's  or  sheep's  head  from  a  butcher.  Dissect 
away  the  skin  and  muscles  covering  the  cranium.  Then  with  a 
small  saw  very  carefully  divide  the  bones  in  a  circular  direction, 
so  as  to  cut  off  those  of  the  crown  of  the  head.  Next  carefully 
remove  the  loosened  bones  of  the  top  of  the  skull,  tearing  them  away 


300  THE  HUMAN  BODY. 

from  the  dura  mater  lining  them.     So  far  the  specimen  may  be  pre> 
pared  previous  to  the  meeting  of  the  class. 

b.  To  the  class  demonstrate  the  tough  dura  mater  enveloping  the 
brain;  then  cut  it  away,  noting  the  processes  which  it  sends  between 
the  two  cerebral  hemispheres  and  between  cerebellum  and  cerebral 
hemispheres.     Then  cut  the  membrane  away. 

c.  Note  its  glistening  inner  surface,  due   to  the  arachnoid  lining 
it;  the  pia  mater  full  of  blood-vessels  and  closely  attached  to  the 
brain;  the  glistening  arachnoid    layer  covering  the  exterior  of  the 
pia  mater.     Then  put  the  specimen  aside  in  alcohol  for  a  day  or 
two.     This  will  harden  the  brain  substance. 

d.  When  the  brain  has  become  somewhat  hardened  dissect  away 
the  pia  mater  on  one  side.      Show  the  cerebral  hemispheres  and 
their  surface   convolutions,  the   cerebellum    and   its  foldings,  the 
medulla  oblongata  beneath  the  cerebellum. 

e.  With  bone  forceps  cut  away  the  remainder  of  the  sides  and  roof 
of  the  skull.     Then  raise  the  brain  in  front,  and  cutting  through  the 
vessels,  nerves,  etc.,  which  attach  it  to  the  base  of  the  skull,  en- 
tirely remove  it  from  the  skull  cavity.     On  it  demonstrate  the  cere- 
bral hemispheres  (which  overlap  the   cerebellum    much  less   than 
in  man),  cerebellum,  mid-brain,  etc. 

/.  Attached  to  the  base  of  the  brain  will  be  found  the  stumps  of 
some  of  the  cranial  nerves,  though  most  of  these  will  have  been  en- 
tirely torn  off  unless  the  dissector  has  some  technical  skill.  The 
optic  commissure,  with  the  optic  tracts  leading  to  it  and  the  stumps 
of  the  optic  nerves  leading'from  it,  will  almost  certainly  be  found. 

g.  Make  sections  across  the  brain  in  different  directions  to  see  the 
gray  matter  spread  over  most  of  its  surface,  and  the  nodules  of  gray 
matter  imbedded  in  its  interior. 


CHAPTEK  XX. 

THE  GENERAL  PHYSIOLOGY   OF  THE   NERVOUS 
SYSTEM. 

The  Properties  of  the  Nervous  System,— If  one's  finger 
unexpectedly  touches  a  very  hot  object,  pain  is  felt  arid  the 
hand  is  suddenly  snatched  away ;  that  is  to  say,  sensation 
is  aroused  and  certain  muscles  are  caused  to  contract.  If, 
however,  the  nerves  passing  from  the  arm  to  the  spinal 
cord  have  been  divided,  or  if  they  have  been  rendered  in- 
capable of  activity  by  disease,  no  such  results  follow.  Pain 
is  not  then  felt  on  touching  the  hot  body  nor  does  any 
movement  of  the  limb  occur ;  even  more,  under  such  cir- 
cumstances the  strongest  effort  of  the  Will  of  the  individual 
is  unable  to  cause  any  movement  of  his  hand.  If,  again, 
the  nerves  of  the  limb  have  connection  with  the  spinal 
cord,  but  parts  of  the  cord  are  injured  higher  up,  between 
the  brain  and  the  point  of  junction  of  the  nerves  of  the 
arm  with  the  cord,  then  contact  with  the  hot  object  may 
cause  the  hand  to  be  snatched  away,  but  no  pain  or  other 
sensation  due  to  the  contact  will  be  felt,  nor  can  the  will 
act  upon  the  muscles  of  the  arm,  either  to  make  them  con- 
tract or  to  prevent  their  contraction.  From  the  compari- 
son of  what  happens  in  such  cases  (which  have  been  observed 
again  and  again  upon  wounded  or  diseased  persons),  with 
what  occurs  in  the  natural  condition  of  things,  several  im- 
portant conclusions  may  be  reached: 

What  usually  results  when  a  hot  object  is  unexpectedly  touched? 
Under  what  circumstances  clo  these  results  not  occur?  Can  the  Will 
cause  movement  of  the  muscles  of  an  arm  whose  nerves  have  been 
cut?  When  the  arm-nerves  are  intact  but  the  spinal  cord  is  injured 
near  the  brain,  what  happens  on  touching  a  hot  body? 


302  THE  HUMAN  BODY. 

1.  The  feeling  of  pain  does  not  reside  in  the  burned  part 
itself;  for  it  is  found  that  applying  a  hot  object  to  the  skin 
or  pinching  it  arouses  no  sensation  if  the  nerves  between 
the  skin  and  the  nerve-centres  be  diseased  or  divided. 

2.  The  hot  object  when  the  nerves  are  intact  originates 
some  change  which,  propagated  along  the  nerves,  excites  a 
condition  of  the  nerve-centres  accompanied  by  a  feeling,  in 
this  particular  case  a  painful  one.     This  is  clear  from  the 
fact  that  loss  of  sensation  immediately  follows  division  of 
the  nerves  of  the  limb,  but  does  not  immediately  follow  the 
injury  of  any  of  its  other  parts.     The  change  propagated 
along   the  nerve-trunks  and  causing  them  to  excite   the 
nerve-centres  is  called  a  nervous  impulse. 

3.  When  a  nerve  in  the  skin  is  excited  it  does  not  direct- 
ly call  forth  muscular  contractions;  for  if  so,  touching  the 
hot  object  would  cause  the  limb  to  be  moved  even  when 
the  nerve  had  been  divided  high  up  in  the  arm,  while,  as  a 
matter  of  observation  and  experiment,  we  find  that  no  such 
result  follows  if  the  nerve-fibres  have  been  cut  in  any  part 
of  their  course  from  the  excited,  or,  in  physiological  phrase, 
the  stimulated,  part  to  the  spinal  marrow.     It  is-  therefore 
through  the  nerve-centres  that  the  nervous  impulse  trans- 
mitted from  the  excited  part  of  the  slcin  is  "  reflected"  or 
sent  lack  to  act  upon  the  muscles. 

4.  The  preceding  fact  makes  it  probable  that  nerve-fibres 

How  do  we  know  that  our  feeling  of  pain  does  not  reside  in  a 
burned  or  pinched  part  of  the  skin? 

What  does  a  touched  hot  object  originate  when  the  nerves  are 
healthy?  What  is  a  "nervous  impulse"? 

Does  a  skin-nerve  when  excited  produce  directly  a  muscular 
movement?  Give  reason  for  your  answer.  What  happens  to  the 
nervous  impulse  transmitted  from  the  excited  part  of  the  skin? 

Is  it  probable  that  other  nerve-fibres  than  those  arising  from  the 
skin  are  connected  with  the  nerve-centres  ? 


FUNCTIONS  OF  NERVES  AND  NERVE-CENTRES.  303 

pass  from  the  centre  to  muscles  as  well  as  from  the  skin  to 
the  centre.  This  is  confirmed  when  we  find  that  if  the 
nerves  of  the  limb  be  divided  the  Will  is  unable  to  act 
upon  its  muscles,  showing  that  these  are  excited  to  con- 
tract through  their  nerves.  That  the  nerve-fibres  con- 
cerned in  arousing  sensation  and  muscular  contractions  are 
distinct,  is  shown  also  by  cases  of  disease  in  which  the 
sensibility  of  the  limb  is  lost  while  the  power  of  voluntarily 
moving  it  remains;  and  by  other  cases  in  which  the  op- 
posite is  seen,  objects  touching  the  hand  being  felt,  while  it 
cannot  be  moved  by  the  Will.  We  conclude  therefore  that 
certain  nerve-fibres  when  stimulated  transmit  something  (a 
nervous  impulse)  to  the  centres,  and  that  these,  when  ex- 
cited by  the  nervous  impulse  conveyed  to  them,  may  radiate 
impulses  through  other  nerve-fibres  to  distant  parts,  the 
centre  serving  as  a  connecting  link  between  the  fibres  which 
carry  impulses  from  without  in,  and  those  which  convey 
them  from  within  out. 

5.  Further  we  conclude  that  the  spinal  cord  can  act  as 
an  intermediary  between  the  fibres  carrying  in  nervous  im- 
pulses and  those  carrying  them  out,  but  that  sensations  can- 
not be  aroused  by  impulses  reaching  the  spinal  cord  only, 
nor  has  the  Will  its  seat  there  ;  volition  and  consciousness 
are  dependent  upon  states  of  the  brain.  This  follows  from 
the  unconscious  movements  of  the  limb  which  follow  stimu- 
lation of  its  skin  after  such  injury  to  the  spinal  cord  as 
prevents  the  transmission  of  nervous  impulses  farther  on; 

Point  out  a  fact  tending  to  prove  that  the  muscles  are  normally 
excited  to  contraction  through  their  nerves.  State  facts  showing 
that  the  nerves  of  sensation  and  those  governing  the  muscles  are 
distinct.  What  purpose  does  the  nerve-centre  serve? 

What  further  conclusions  may  we  draw  from  the  facts  already 
considered  in  this  chapter?  Give  reasons  for  your  answer. 


304  THE  HUMAN  BODY. 

from  the  absence,  in  such  cases,  of  sensation  in  the  part 
whose  nerves  have  been  injured;  and  from  the  loss  of  the 
power  of  voluntarily  causing  its  muscles  to  contract. 

6.  Finally,  we  conclude  that  the  spinal  cord  in  addition 
to  being  a  centre  for  unconscious  movements  serves  also  to 
transmit  nervous  impulses  to  and  from  the  brain;  this  is 
confirmed  by  the  histological  observation  that  in  addition 
to  the  nerve-cells,  which  are  the  characteristic  constituents 
of  nerve-centres,  it  contains  the  simply  conductive  nerve- 
fibres,  many  of  which  pass  on  to  the  brain.  In  other  words 
the  spinal  cord,  besides  containing  fibres  which  enter  it 
from,  and  pass  from  it  to,  the  skin  and  muscles,  contains 
many  fibres  which  unite  it  to  other  centres. 

The  Functions  of  Nerve-Centres  and  Nerve-Trunks, — 
From  what  has  been  stated  in  the  previous  paragraphs  it  is 
clear  that  we  may  distinctly  separate  the  nerve-trunks  from 
the  nerve-centres.  The  fibres  serve  simply  to  convey  im- 
pulses either  from  without  to  a  centre  or  in  the  opposite 
direction,  while  the  centres  conduct  and  do  much  more. 
They  take  heed,  some  consciously  and  some  unconsciously, 
of  the  impulses  carried  to  them  by  the  ingoing  nerve-fibres, 
and  then  send  out  impulses  along  outgoing  nerve-fibres; 
these  impulses  call  into  action  the  proper  organs  for  the 
safety  and  well-being  of  the  body  in  general.  The  centres 
do  not  merely  transmit  and  reflect,  they  also  co-ordinate. 

Classification  of  Nerve-Fibres. — The  nerve-fibres  of  the 
body  fall  into  two  great  groups  corresponding  to  those 

'For  what  is  the  spinal  cord  a  centre?  What  else  does  it  do? 
How  does  histology  support  the  belief  that  the  spinal  cord  is  both 
a  nerve-centre  and  &  conductor  of  nervous  impulses? 

What  is  the  function  of  nerve-fibres?  What  is  done  by  nerve- 
centres  in  addition  to  conducting  nerve-impulses? 

Into  what  main  groups  may  nerve  fibres  be  classified? 


PSYCHIC  NERVE-CENTRES.  305 

which  carry  impulses  to  the  centres  and  those  which  carry 
them  out  from  the  centres.  The  former  are  called  afferent 
or  sensory  fibres  and  the  latter  efferent  or  motor. 

The  posterior  roots  of  the  spinal  nerves  contain  only 
afferent,  the  anterior  only  efferent,  nerve-fibres- 

Classification  of  Nerve-Centres,— Nerve-centres  are  of 
three  kinds:  (1)  Automatic  centres,  which;  without~Demg~ 
excited  by  the  action  of  any  sensofyTferve  or  by  the  Will^ 
originate  in  themselves  stimuli  for  efferent  nerves.  (2)  Re- 
flex centres,  which  act  quite  independently  of  the  Will  and 
of  consciousness,  but  are  aroused  by  the  action  of  a  nervous 
impulse  conveyed  to  them  by  a  sensory  nerve,  and  in  turn 
excite  one  or  more  efferent  nerves.  (3)  Conscious  or  psy- 
chic centres,  whose  activity,  however  aroused,  is  accom- 
panied by  some  kind  of  mental  activity;  as  feeling,  or 
willing,  or  reasoning. 

The  Psychic  Nerve-Centres  lie  in  the  fore-brain,  and 
mainly  in  the  gray  matter  of  its  convolutions.  If  the  cere- 
bral hemispheres  of  a  pigeon  be  destroyed  and  all  the  rest  of 
its  body  left  intact,  the  animal  can  still  control  its  muscles 
so  as  to  execute  many  movements,  but  it  gives  no  sign  of 
consciousness.  Left  to  itself  it  will  stand  still  until  it  dies; 
corn  and  drink  placed  before  it  arouse  in  it  no  idea  of  eat- 
ing; it  will  die  of  starvation  surrounded  by  food.  Yet  it 
can  move  all  its  muscles,  and  if  food  is  placed  in  its  mouth 
will  swallow  it.  If  its  tail  be  pulled  it  will  walk  forward; 


What  fibres  are  found  in  the  posterior  spinal  nerve-roots?  What 
in  the  anterior? 

Name  the  main  varieties  of  nerve-centres.  What  is  done  by 
automatic  centres?  What  by  reflex?  What  is  the  characteristic 
property  of  the  psychic  centres? 

Where  are  the  psychic  nerve-centres  located?  What  may.be  ob- 
served in  a  pigeon  whose  cerebral  hemispheres  have  been  destroyed? 


306  THE  HUMAN  BODY. 

if  it  be  put  on  its  back  it  will  get  on  its  feet;  if  it  be 
thrown  into  the  air  it  will  fly  until  it  strikes  against  some- 
thing on  which  it  can  alight;  if  its  feathers  be  ruffled  it 
will  smooth  them  with  its  bill. 

The  difference  between  a  pigeon  in  this  state  and  an 
uninjured  pigeon  lies  in  the  absence  of  the  power  of  form- 
ing ideas  or  initiating  movements.  It  has  no  thoughts,  no 
ideas,  no  Will.  We  cannot  predict  what  an  uninjured 
pigeon  will  do  under  given  circumstances:  we  can  say  be- 
forehand what  the  pigeon  with  no  cerebral  hemispheres 
will  do;  it  is  a  mere  machine  or  instrument,  which  can  be 
played  upon.  In  such  a  pigeon  the  excitation  of  any  given 
sensory  nerve  or  nerves  excites  unconscious  nerve-centres 
which  set  certain  muscles  at  work,  ai;d  the  result  of  any 
one  stimulus  is  always  the  same  invariable  movement. 
The  animal  exhibits  no  evidence  of  possessing  any  con- 
sciousness ;  it  has  no  desires  or  emotions  ;  it  is  like  a  piano 
which  while  untouched  is  silent,  but  when  a  given  key  is 
struck  emits  always  the  same  note  ;  so  the  pigeon  without 
its  cerebral  hemispheres  stays  quiet  while  left  to  itself,  and 
responds  to  any  one  given  stimulus  always  in  one  invari- 
able and  predicable  way. 

Functions  of  the  Cerebellum. — The  cerebellum  is  the 
great  centre  for  co-ordinating  the  muscles  of  locomotion. 
Each  step  we  take  implies  the  action  of  many  muscles  and 
many  thousands  of  muscular  fibres;  the  actions  of  all  must 
be  very  precisely  graded  as  to  amount,  and  very  accurately 
arranged  as  to  proper  sequence./We  do  not,  however,  con- 
sciously think  about  the  muscles  to  be  used  in  every  move- 
How  does  such  a  pigeon  differ  from  an  uninjured  pigeon? 
What  is  the  main  function  of  the  cerebellum?     What  is  implied 
in  each  step  that  we  take? 


FUNCTIONS  OF  THE  CEREBELLUM.  307 


_ment  of  each  step;  if  we  do  think  at  all  about  our  walking 
)  the  cerebral  hemispheres  simply  send  a  message  to  the  cere- 
ibelium,  and  leave  it  (witH  the  aid  of  the  spinal  cord)  to 
regulate  all  the  details.  When  we  walk  without  thinking 
about  it,  the  contact  of  the  foot  with  the  ground  stimulates 
sensory  nerves  of  the  sole,  which  then  stimulate  the  locomotor 
centres;  these  centres  excite  in  proper  order  the  nerves 
which  control  the  muscles;  and  the  co-ordinated  action  of 
the  muscles  produces  the  next  step7~7' 

A  pigeon  with  its  cerebellum—destroyed  and  all  the  rest 
of  its  nervous  system  intact  stands  unsteadily,  staggers  when 
it  attempts  to  walk,  and  flutters  uselessly  when  thrown 
into  the  air.  But,  having  its  cerebrum,  it  wills  and  feels; 
it  does  not  stand  quiet  until  touched;  it  initiates  movements 
when  left  to  itself,  though  it  cannot  perform  them  properly. 
It  wills,  and  feels,  and  thinks,  but  cannot  co-ordinate  the 
action  of  its  muscles  except  for  some  simple  movements, 
regulated  by  the  medulla  oblongata  or  the  spinal  cord. 

Automatic  Nerve-Centres  send  out  nervous  impulses 
through  efferent  nerves  without  waiting  to  be  excited  by 
afferent  nerves  or  by  the  Will.  The  most  conspicuous  are 
the  small  nerve-centres  buried  in  the  heart,  which  excite  its 
beat  even  when  it  is  separated  from  all  the  rest  of  the  body. 
Another  automatic  centre  is  that  which  lies  in  the  medulla 
oblongata  and  stimulates  the  nerves  which  control  the 

Do  we  have  to  think  about  using  each  muscle  concerned  in  walk- 
ing? What  happens  when  we  think  about  our  walking?  What  when 
we  walk  without  thinking  about  it  ? 

What  do  we  see  in  a  pigeon  whose  cerebellum  has  been  destroyed? 
Does  it  initiate  movements?  Does  it  execute  them  well?  What  is 
its  condition  as  regards  willing,  feeling,  and  thinking?  What  can 
it  not  do? 

What  is  done  by  automatic  nerve-centres?  Give  examples  of  au- 
tomatic nerve-centres. 


308  THE  HUMAN  BODY. 

muscles  of  respiration.  When  this  centre  is  cut  off  from 
all  sensory  nerves  it  still  acts,  and  its  activity  goes  on  even 
against  the  Will.  We  can  voluntarily  hold  the  breath  for 
a  short  time,  but  not  long  enough  to  kill  ourselves  by  suffo- 
cation. Although  automatic  nerve-centres  act  indepen- 
dently of  impulses  carried  to  them  by  nerve-trunks,  they 
are  nevertheless  usually  more  or  less  subject  to  control  by 
them.  For  example,  stimulating  the  branch  of  the  pneu- 
mogastric  nerve  (p.  293)  which  goes  to  the  automatic  heart 
nerve-centres  slows  the  beat  of  the  organ;  and  a  dash  of 
cold  water  on  the  skin  makes  us  draw  a  deep  breath. 

Reflex  Centres  are  aroused  to  activity  by  nervous  im- 
pulses conveyed  to  them  through  afferent  nerves:  they 
then  excite  efferent  nerves  and  produce  a  movement  or  a 
secretion.  Such  nerve-centres  do  all  the  routine  of  the  ad- 
ministrative control  of  the  organs  of  the  body,  without 
troubling  the  psychic  centres.  They  frequently  act  with- 
out the  intervention  of  consciousness  at  all,  and  often  in 
spite  of  the  Will.  When  sugar  is  placed  in  the  mouth  it 
excites  its  sensory  nerves  ;  these  stimulate  a  centre  from 
which  nerves  go  to  the  salivary  glands,  and  these  nerves, 
aroused  by  the  centre,  make  the  gland-cells  secrete  and  pour 
saliva  into  the  mouth;  no  effort  of  the  Will  can  stop  this 
reflex  action,  so  called  because  a  nervous  impulse  sent  to  a 
centre  by  one  set  of  nerve-fibres  is  turned  back  or  reflected 
from  it  along  another  set.  When  a  morsel  of  food  enters 
the  pharynx  it  excites  the  sensory  nerves  of  the  mucous 

Can  a  man  commit  suicide  by  holding  his  breath?  Are  the 
automatic  centres  entirely  free  from  control?  Illustrate? 

How  are  reflex  centres  excited?  What  is  the  consequence  of 
their  stimulation?  "What  sort  of  work  in  the  body  is  executed  by 
reflex  nerve-centres?  Are  we  always  conscious  of  their  action?  Can 
the  Will  always  control  them?  What  happens  when  sugar  is  placed 
on  the  tongue?  Why  is  it  called  a _H  reflex  action"? 


USES  OF  AUTOMATIC  NER VE- CENTRES.         309 

membrane;  these  arouse  a  reflex  centre  of  swallowing, 
which  sends  out  nervous  impulses  to  the  swallowing  mus- 
cles, and  the  food  is  sent  on  into  the  gullet  whether  we  wish 
it  or  not.  Sneezing  when  something  irritates  the  mucous 
membrane  of  the  nose,  and  coughing  where  some  foreign 
mass  enters  the  larynx,  are  other  instances  of  reflex  actions. 

The  Use  of  Automatic  and  Reflex  Centres  is  to  relieve 
the  thinking  centres  of  the  vast  amount  of  work  which 
would  be  thrown  upon  them  if  every  action  of  the  body 
each  moment  had  to  be  planned  and  willed.  Were  not  the 
unconscious  regulating  nerve-centres  always  at  work  the 
mind  would  be  overburdened  by  the  mass  of  business  which 
it  would  have  to  look  after  every  minute.  No  time  would 
be  left  for  intellectual  development  if  we  had  to  think 
about  and  to  will  each  heart-beat,  each  inspiration  and  ex- 
piration, and  the  swallowing  of  each  mouthful  of  food. 
Moreover,  during  sleep,  so  necessary  for  the  rest  and  repair 
of  the  psychic  centres,  the  automatic  and  reflex  centres 
carry  on  the  actions  essential  for  the  nutrition  of  the  body 
and  the  maintenance  of  life.  If  we  had  to  reason  concern- 
ing each  beat  of  the  heart  and  decide  if  it  was  time  for  it 
to  occur  and  what  force  it  should  have,  and  then  to  make  up 
our  minds  whether  to  will  it  or  not,  we  could  never  sleep. 

Habits  are  Acquired  Reflex  Actions,  distinguished  from 
primary  or  those  born  with  us,  such  as  sneezing,  coughing, 
and  winking.  Every  time  a  nerve-centre  acts  in  a  given  way 
it  tends  to  more  easily  act  in  that  manner  again;  as  a  result 

Give  other  examples  of  reflex  actions. 

What  is  the  main  use  of  th<3  automatic  and  reflex  nerve-centres? 
What  would  result  if  the  unconscious  nerve-centres  were  not  always 
at  work? 

What  are  habits?  What  happens  when  a  nerve-centre  acts  in  a 
given  manner?  What  is  the  result? 


310  THE  HUMAN  BODY. 

many  actions  which  are  at  first  only  performed  with 
trouble  and  thought  are  after  a  time  executed  easily  and 
unconsciously.  The  act  of  walking  is  a  good  instance;  each 
of  us  in  infancy  learned  to  walk  with  much  pains  and  care, 
thinking  about  each  step.  But  the  more  we  walked  the 
closer  became  ingrained  in  the  nervous  system  the  connec- 
tion between  the  stimulation  of  nerves  in  the  sole  when  a 
foot  touched  the  ground,  and  the  sending  out  by  the  reflex 
nerve-centres  with  which  they  were  in  connection,  of 
impulses  to  those  muscles  which  had  to  make  the  next  step. 
At  last  the  contact  of  the  foot  with  the  ground,  stimu- 
lating some  sensory  nerves,  acts  so  readily  on  the  "  nerve- 
centres  of  walking"  that  the  cerebral  hemispheres  need 
take  no  heed  about  it:  we  walk  ahead  while  thinking 
of  something  else.  In  other  words  we  have  acquired  a 
reflex  action  not  born  in  us.  Other  instances  will  readily 
come  to  mind:  as  the  difficulty  with  which  AVC  learned  to 
ride,  or  swim,  or  skate,  thinking  about  and  willing  each 
movement;  and  the  ease  with  which  we  do  all  these  things 
after  a  little  practice.  The  trained  lower  nerve-centres  then 
do  all  the  co-ordinating  work  and  the  Will  has  no  more  need 
to  trouble  about  the  matter.  A  habit  simply  means  that  the 
unconscious  parts  of  the  nervous  system  have  been  trained 
to  do  certain  things  under  given  conditions,  and  can  only  be 
restrained  from  doing  them  by  a  special  effort  of  the  con- 
scious Will.  A  practised  rider  will  keep  his  seat  uncon- 
sciously under  all  ordinary  circumstances,  and  can  only 
fall  off  his  horse  by  taking  some  trouble  to  do  so,  by  will- 
ing it  in  fact;  an  unskilled  rider,  on  the  other  hand,  must 
exert  all  his  attention  to  avoid  falling.  So  with  what  in 

Illustrate  by  the  act  of  walking.     Give  other  examples.     What 
does  a  " formed  habit"  really  mean?    Illustrate. 


EJGIENE  OF  THE  BRAIN.  311 

every-day  language  are  called  "  habits":  once  we  have  repeat- 
ed an  action  so  often  that  our  bodies  almost  unconsciously 
do  it,  it  becomes  a  habit,  and  needs  special  exercise  of  Will 
to  deviate  from  it.  We  thus  find,  in  the  tendency  of  the 
nervous  system  to  go  on  doing  what  it  has  been  trained  to 
do,  a  physiological  reason  for  endeavoring  to  form  good 
and  to  avoid  bad  habits  of  whatever  sort,  physiological, 
business,  social,  or  moral.  Every  thought,  every  action, 
leaves  in  the  nervous  system  its  result  for  good  or  ill.  The 
more  often  we  yield  to  temptation  the  stronger  effort  of 
the  Will  is  required  to  resist  it.  The  knowledge  that  every 
weak  yielding  degrades  our  nerve-organs  and  leaves  its  trail 
in  the  brain,  through  whose  action  man  is  the  "para- 
gon of  animals,"  while  every  resistance  makes  less  close  the 
bond  between  the  feeling  and  the  act  for  all  future  time, 
ought  surely  to  "give  us  pause";  on  the  other  hand,  every 
resistance  of  temptation  helps  to  make  subsequent  resist- 
ance easier. 

Hygiene  of  the  Brain. — The  brain,  like  the  muscles,  is 
improved  and  strengthened  by  exercise  and  injured  by  over- 
work or  idleness;  and  just  as  a  man  may  specially  develop 
one  set  of  muscles  and  neglect  the  rest  until  they  degenerate, 
so  he  may  do  with  his  brain;  developing  one  set  of  intel- 
lectual faculties  and  leaving  the  rest  to  lie  fallow  until,  at 
last,  he  almost  loses  the  power  of  using  them  at  all.  The 
fierceness  of  the  battle  of  life  nowadays  especially  tends  to 
produce  such  lopsided  mental  development.  How  often 


What  happens  when  we  have  very  frequently  repeated  an  action? 
Point  out  why  it  is  desirable,  even  on  physiological  grounds,  to  form 
good  habits.  How  does  every  thought  or  act  influence  the  nervous 
system?  What  is  the  consequence  of  yielding  to  temptation?  What 
of  resisting  it? 


312  THE  HUMAN  BODY. 

does  one  meet  the  business  man,  so  absorbed  in  money- 
getting  that  he  has  lost  all  power  of  appreciating  any  but 
the  lower  sensuous  pleasures;  the  intellectual  joys  of  art, 
science,  and  literature  have  no  charm  for  him;  he  is  a  mere 
money-making  machine.  One,  also,  not  unfrequently 
meets  the  scientific  man  with  no  appreciation  of  art  or 
literature;  and  literary  men  utterly  incapable  of  sympathy 
with  science.  A.  good  collegiate  education  in  early  life, 
on  a  broad  basis  of  mathematics,  literature,  and  natural 
science,  is  the  best  security  against  such  deformed  mental 
growth. 


APPENDIX  TO   CHAPTER  XX. 

1.  Place  a  frog  on  the  table:  note  that  it  sits  up  and  breathes 
(as  shown  by  the  movements  of  its  throat),  and  either  stays  still  or 
jumps  around  as  it  pleases;  i.e.,  it  has  a  Will  of  its  own,  and  its  actions 
cannot  be  predicted. 

2.  Etherize  two  frogs  (note,  p.  68),  removing  them  from  the  ether- 
ized water  the  moment  they  become  insensible.     With  strong  sharp 
scissors  cut  off  from  one  frog  (a)  all  the  head  in  front  of  the  anterior 
margins  of  the  tympanic  membranes:  in  the  other  frog  (J)  remove 
the  head  along  a  line  joining  the  posterior  borders  of  the  tympanic 
membranes.      Place  both  frogs  aside  on  a  dish  containing  a  little 
water  for  half  an  hour.     The  quantity  of  water  should  be  such  that 
while  keeping  the  frogs  moist  it  will  not  reach  to  the  wounds. 

3.  The  frog  (a)  which  has  lost  its  cerebral  hemispheres,  but  re- 
tained its  mid  brain,  cerebellum,  and  medulla  oblongata,  will  be 
found  after  the  above-stated  time  sitting  up  in  a  natural  position,  and 
breathing.     Left  to  itself  it  will,  however,  never  walk  or  jump;  it 
shows  no  sign  of  possessing  a  will.     Its  heart  continues  to  beat  and 
its  respiratory  muscles  to  contract,  but  left  alone  it  stays  where  it  is. 
Turned  upon  its  back  it  will  regain  its  feet;  and  put  into  water  it 
will  swim:  its  muscles,  and  the  nerves  controlling  them,  are,  there- 
fore, quite  able  to  act.    The  animal  stays  still  not  because  the  parts  of 
its  body  necessary  to  produce  movements  are  injured,  but  because  it 
can  no  longer  will  a  movement.    Such  a  frog  shows  very  well  the  de- 
pendence of  volition  upon  the  presence  of  the  cerebral  hemispheres. 


APPENDIX.     CHAPTER  XX.  313 

4.  The  frog  (b)  will  have  had  its  whole  brain  removed.     Its  heart 
will  continue  to  beat,  but  its  breathing  movements  will  cease,  be- 
cause the  respiratory  centre,  which  lies  in  the  medulla  oblongata,  has 
been  cut  away.     It  will  also  lie  down  squat,  instead  of  sitting  up 
like  a  normal  frog,  because  its  most  important  muscle  co-ordinating 
centres  have  been  removed  with  the  mid-brain  and  cerebellum.     Left 
to  itself  the  animal  will,  within  half  an  hour  of  the  removal  of  the 
head,  pull  up  its  hind  legs  into  their  natural  position,  but  after  this 
it  will  make  no  movement.     It  has  no  volition. 

5.  Such  a  frog  can,  however,  perform  many  co-ordinated   reflex 
actions,  which  may  be  illustrated  as  follows:  (a)  Pinch  a  toe;  it  will 
be  pulled  away,      (b)   Soak   some    blotting-paper  in  vinegar,    and 
then  cut  the  paper  into  small  pieces  about  |  inch  square.     Put  these 
bits  of  paper  on  different  regions  of  the  frog's  skin,  dipping  the  ani- 
mal in  clean  water  after  each  application,  to  wash  away  the  vinegar. 
It  will  be  found  that  the  brainless  creature  moves  its  limbs  so  as  to 
wipe  away  the  acid  paper  placed  on  its  skin.     The  frog  without  its 
brain  has  no  Will  and  no  consciousness;  but  its  spinal  cord  when  ex- 
cited by  afferent  nerves,  whose  ends  the  vinegar  stimulates,  excites 
in   turn  efferent   nerves   which  stimulate   muscles,  whose   contrac- 
tion produces  a  movement  calculated  to  rub  away  the  irritating 
object. 

6.  Now  run  a  stout  pin  down  the  frog's  neural  canal  so  as  to  de- 
stroy its  spinal  cord.    It  will  be  found  that  no  subsequent  pinching  of 
the  creature  or  putting  of  vinegar  on  its  skin  causes  any  movement. 
Its  muscles  and  nerve-trunks  are  intact,  but  the  spinal  reflex  centre, 
which  in  the  previous  experiments  was  excited  by  afferent  nerves, 
and  then  in  turn  stimulated  efferent  nerves,  is  destroyed.     The  heart 
continues  to  beat,  on  account  of  the  automatic  nerve-centres  in  it; 
but  no  voluntary  and  no  reflex  actions  are  exhibited  by  the  animal. 

7.  The  nerve-trunks  and   the  muscles  are,  however,  still  active. 
Turn  the  frog  on  its  back  and  carefully  expose  (p.  299)  the  origins  of 
the  sciatic  nerves.     On  pinching  these,  the  muscles  of  the  leg  will  be 
seen  to  contract.     The  irritation  of  the  nerve  by  the  pinch  starts  in 
it  a  nervous  impulse  which  travels  down  the  nerve -branches  to  the 
muscles. 


CHAPTEE  XXL 

THE  SENSES. 

Common  Sensation  and  Special  Senses. — Changes  in 
many  parts  of  our  bodies  are  accompanied  or  followed  by 
states  of  consciousness  which  we  call  sensations.  All 
such  parts  (sensitive  parts)  are  in  connection,  direct  or  in- 
direct, with  the  brain  by  sensory  nerve-fibres.  Since  all  feel- 
ing is  lost  in  any  region  of  the  body  when  this  connecting 
path  is  severed,  it  is  clear  that  all  sensations,  whatever  their 
primary  exciting  cause,  are  finally  dependent  on  conditions 
of  the  brain.  Since  all  nerves  lie  within  the  body  as  circum- 
scribed by  the  skin,  one  might  be  inclined  to  suppose  that  the 
cause  of  all  sensations  would  appear  to  be  within  our  bodies 
themselves;  that  the  thing  felt  would  be  recognized  as  a 
modification  of  some  portion  of  the  person  feeling.  This  is 
the  case  with  regard  to  many  sensations:  a  headache,  tooth- 
ache, or  earache  gives  us  no  idea  of  any  external  object ;  it 
merely  suggests  to  each  one  a  particular  state  of  a  sensitive 
portion  of  himself.  As  regards  many  sensations  this  is  not 
so;  they  suggest  to  us  external  causes,  to  properties  of  which, 
and  not  to  states  of  our  bodies,  we  ascribe  them;  and  so  they 
lead  us  to  the  conception  of  an  external  universe  in  which  we 
live.  A  knife  laid  on  the  skin  produces  changes  in  it  which 

With  what  are  all  sensitive  parts  of  the  body  in  connection  ?  By 
what  nerve-fibres?  How  do  we  know  that  all  sensations  finally  de- 
pend on  the  brain? 

Why  might  we  suppose  that  the  causes  of  all  sensations  would 
seem  to  lie  within  the  bocty?  Name  sensations  merely  suggesting 
to  us  a  state  of  the  body  itself.  What  do  some  other  sensations  sug- 
gest to  us?  Illustrate. 


COMMON  SENSATIONS.  315 

lead  us  to  think  not  of  a  state  of  the  skin,  but  of  proper- 
ties of  some  object  outside  the  skin;  we  believe  we  feel  a 
cold  heavy  hard  thing  which  is  not  the  skin.  We  have, 
however,  no  sensory  nerves  going  into  the  knife  and  inform- 
ing us  directly  of  its  condition;  what  we  really  feel  are  the 
modifications  of  the  body  produced  by  the  knife,  although 
we  irresistibly  think  of  them  as  properties  of  the  knife — of 
some  object  that  is  no  part  of  the  body.  Let  now  the  knife 
cut  through  the  skin;  we  feel  no  more  knife,  but  ex- 
perience pain,  which  we  think  of  as  a  condition  of  our- 
selves. We  do  not  say  the  knife  is  painful,  but  that  the 
finger  is,  and  yet  we  have,  so  far  as  sensation  goes,  as  much, 
reason  to  call  the  knife  painful  as  cold.  Applied  one  way 
it  produced  local  changes  in  the  skin  arousing  a  sensation  of 
cold,  and  in  another  local  changes  causing  a  sensation  of  pain. 
Nevertheless  in  the  one  case  we  speak  of  the  cold  as  being 
in  the  knife,  and  in  the  other  of  the  pain  as  being  in  the 
finger. 

Sensitive  parts,  such  as  the  surface  of  the  skin,  through 
which  we  get,  or  believe  we  get,  information  about  outer 
things,  are  of  far  more  intellectual  value  to  us  than  sensi- 
tive parts,  such  as  the  subcutaneous  tissue  into  which  the 
knife  may  cut,  which  only  give  us  sensations  referred  to 
conditions  of  our  own  bodies.  The  former  arc  called  Organs 
of  Special  Sense  ;  the  latter  are  parts  endowed  with  Common 
Sensation. 

Common  Sensations  are  quite  numerous ;  for  example, 
pain,  hunger,  nausea,  thirst,  satiety,  and  fatigue. 


What  is  meant  by  "organs  of  some  special  sense"?    What  by 
parts  endowed  with  common  sensation? 
Name  some  common  sensations. 


316  THE  HUMAN  BODY. 

Hunger  and  Thirst. — These  sensations  regulate  the  tak- 
ing of  food.  Local  conditions  play  a  part  in  their  produc- 
tion, but  general  states  of  the  body  are  also  concerned. 

Hunger  in  its  first  stages  is  due  to  a  condition  of  the 
gastric  mucous  membrane  which  comes  on  when  the  stom- 
ach has  been  empty  some  time;  it  may  then  be  tempo- 
rarily stilled  by  filling  the  stomach  with  indigestible  sub- 
stances. But  soon  the  feeling  comes  back  intensified  and 
can  only  be  allayed  by  the  ingestion  of  nutritive  materials; 
provided  these  are  absorbed  and  reach  the  blood  their  mode 
of  entry  is  unessential;  hunger  may  be  stayed  by  injections 
of  food  into  the  intestine  as  completely  as  by  filling  the 
stomach  with  it. 

Similarly,  thirst  maybe  temporarily  relieved  by  moisten- 
ing the  throat  without  swallowing,  but  then  soon  returns ; 
while  it  may  be  permanently  relieved  by  water  injections 
into  the  veins,  without  wetting  the  throat  at  all. 

Both  sensations  depend  in  part  on  local  conditions 
of  sensory  nerves,  but  may  be  more  powerfully  excited 
by  poverty  of  the  blood  in  foods  or  water  ;  this  deficiency 
directly  stimulates  the  hunger  and  thirst  centres  of  the 
brain. 

The  Special  Senses  are  commonly  described  as  five  in 
number,  but  there  are  at  least  six;  namely,  sight,  hearing, 
touch,  the  temperature  sense,  smell,  and  taste. 


To  what  is  the  first  stage  of  hunger  due?  How  may  it  be  tempo- 
rarily stayed?  Need  food  enter  the  stomach  in  order  to  alleviate 
hunger? 

How  may  thirst  be  temporarily  relieved?  How  permanently 
without  swallowing  water?  On  what  do  the  sensations  of  hunger 
and  thirst  in  part  depend  ?  How  may  they  be  more  powerfully  ex- 
cited? Enumerate  the  special  senses. 


SIGHT.  317 

•  The  Visual  Apparatus  consists  of  nervous  tissues  immedi- 
ately concerned  in  giving  rise  to  sensations,  supported, 
protected,  and  nourished  by  other  parts.  Its  essential  parts 
are,  (1)  the  retina,  a  thin  membrane  lying  in  the  eyeball  and 
containing  microscopic  elements  which  are  so  acted  upon 
by  light  as  to  stimulate  (2)  the  optic  nerve;  this  nerve  ends 
(3)  in  a  part  of  the  brain  (visual  centre)  which  when  stimu- 
lated arouses  in  our  consciousness  a  feeling  or  sensation  of 
sight.  The  visual  centre  may  be  excited  in  very  many  ways, 
and  quite  independently  of  the  optic  nerve  or  the  retina ; 
as  is  frequently  seen  in  delirious  persons,  in  whom  inflamma- 
tion or  congestion  of  the  brain  excites  directly  the  visual 
centre  and  gives  rise  to  visual  hallucinations. 

Usually,  however,  the  cerebral  visual  centre  is  only  ex- 
cited through  the  optic  nerve,  and  the  optic  nerve  only  by 
light  acting  upon  the  retina.  The  eyeball,  containing  the 
retina,  is  so  constructed  that  light  can  enter  it,  and  so  placed 
and  protected  in  the  body  that  as  a  general  thing  no  other 
form  of  energy  can  act  upon  it  so  as  to  stimulate  the  retina. 
Under  exceptional  circumstances  we  may  have  sight-sensa- 
tions when  no  light  reaches  the  eye;  anything  which  stimu- 
lates the  retina,  so  long  as  it  is  connected  by  the  optic  nerve 
with  the  cerebral  visual  centre,  will  cause  a  sight-sensation. 
A  severe  blow  on  the  eye,  even  in  complete  darkness,  will 
cause  the  sensation  of  a  flash  of  light;  the  compression  of  the 
eyeball  excites  the  retina,  the  retina  excites  the  optic  nerve, 

Of  what  does  the  visual  apparatus  consist?  What  are  its  essen- 
tial parts?  What  happens  when  the  visual  centre  is  stimulated? 
Is  it  only  stimulated  by  the  agency  of  light?  Illustrate. 

How  is  the  visual  centre  usually  excited?  Why  is  light  the  form 
of  energy  which  most  of t<m  stimulates  the  retina?  Give  an  example 
of  the  production  of  a  sight-sensation  in  the  absence  of  light.  What 
happens  in  the  nervous  System  when  a  man  "sees  sparks"  on  receiv- 
ing a  blow  in  the  eye? 


318  THE  HITMAN  BOD7. 

the  optic  nerve  the  visual  nerve-centre,  and  the  result  is  a 
sight-sensation.  * 

The  Eye-Socket, — The  eyeball  is  lodged  in  a  bony  cav- 
ity, the  orbit,  open  in  front.  Each  orbit  is  a  pyramidal 
chamber  containing  connective  tissue,  blood-vessels,  nerves, 
and  much  fat ;  the  fat  forms  a  soft  cushion  on  which  the 
back  of  the  eyeball  rolls. 

The  Eyelids  are  folds  of  skin,  strengthened  by  cartilage 
and  moved  by  muscles.  Opening  along  the  edge  of  each  eye- 
lid are  from  twenty  to  thirty  minute  glands,  called  the 
Meibomian  follicles.  Their  secretion  is  sometimes  abnor- 
mally abundant,  and  then  appears  as  a  yellowish  matter 
along  the  edges  of  the  eyelids,  which  often  dries  in  the 
night  and  causes  the  lids  to  be  glued  together  in  the 
morning.  The  eyelashes  are  curved  hairs,  arranged  in  one 

In  what  is  each  eyeball  lodged?    What  does  the  orbit  contain? 

What  are  the  eyelids?  The  Meibomian  glands?  Why  are  the 
eyelids  sometimes  stuck  together  in  the  morning?  What  are  the  uses 
of  the  eyelashes? 

*  The  fact  that  sight-sensations  may  be  aroused  quite  independently  of  all 
light  acting  upon  the  eye  is  paralleled  by  similar  phenomena  in  regard  to  other 
senses,  and  is  of  fundamental  psychological  and  metaphysical  importance. 
That  a  blow  on  the  closed  eye  gives  rise  to  a  vivid  light-sensation,  even  in  the 
absence  of  all  actual  light,  proves  that  our  sensation  of  light  is  quite  a  different 
thing  from  light  itself.  The  visual  sensory  apparatus,  it  is  true,  is  so  con- 
structed and  protected  that  of  all  the  forces  of  nature,  light  m  the  one  which  far 
most  frequently  stimulates  it.  But  as  regards  the  peculiarity  in  the  quality  of 
the  sensation  which  leads  us  to  classify  it  as  "  a  visual  sensation,"  that  pecu- 
liarity has  nothing  to  do  with  any  property  of  light.  The  visual  nerve-centre 
when  stimulated  causes  a  sight-sensation,  whether  it  has  been  excited  by  light, 
or  by  a  blow,  or  by  electricity.  Similarly  the  auditory  brain-centre  gives  us 
a  sound-sensation  when  stimulated  by  actual  external  sound-waves,  or  by  a 
blow  on  the  ear,  or  by  disease  of  the  auditory  organ.  One  kind  of  energy,  light, 
excites  more  often  than  any  other  the  visual  nerve-apparatus;  another,  sound, 
the  auditory  nerve -apparatus;  a  third,  pressure,  the  touch  nerve  organs. 
Hence  we  come  to  associate  light  with  visual  sensations  and  to  think  of  it  as 
something  liKe  our  sight- feelings;  and  to  imagine  sound  as  something  like  our 
auditory  sensations;  and  so  forth.  As  a  matter  of  fact  both  light  and  sound  are 
merely  movements  of  ether  or  air;  it  is  our  own  stimulated  nerve-centres 
which  produce  visual  and  auditory  sensations;  the  ethereal  or  aerial  vibrations 
merely  act  as  the  stimuli  which  arouse  the  nervous  apparatus. 


THE  TEAR  APPARATUS.  319 

or  two  rows  along  each  lid  and  helping  to  keep  dust  from 
falling  into  the  eye;  and,  when  the  lids  are  nearly  closed, 
to  protect  it  from  a  dazzling  light. 

The  Lachrymal  Apparatus  consists  of  the  tear-gland  in 
each  orbit,  of  ducts  which  carry  its  secretion  to  the  upper 
eyelid,  and  of  canals  by  which  this,  unless  when  excessive, 
is  carried  off  from  the  front  of  the  eye  without  running 
down  over  the  face.  The  lachrymal  or  tear  gland,  about 
the  size  of  an  almond,  lies  in  the  upper  and  outer  corner  of 
the  orbit.  It  is  a  compound  racemose  gland,  from  which 
twelve  or  fourteen  ducts  run  and  open  at  the  outer  corner 
of  the  upper  eyelid  on  its  inner  surface.  The  secretion 
there  poured  out  is  spread  evenly  over  the  exposed  part  of 
the  eye  by  the  movements  of  winking,  and  keeps  it  moist ; 
finally  it  is  drained  off  by  two  lachrymal  canals,  one  of 
which  opens  by  a  small  pore  on  an  elevation,  or  papilla, 
near  the  inner  end  of  the  margin  of  each  eyelid.  The  aper- 
ture of  the  lower  canal  can  be  readily  seen  by  examin- 
ing its  papilla  in  front  of  a  looking-glass.  The  canals 
run  inwards  and  open  into  the  lachrymal  sac,  which  lies 
just  outside  the  nose,  in  a  hollow  where  the  lachrymal  and 
superior  maxillary  bones  (Land  MX,  Fig.  16)  meet.  From 
this  sac  the  nasal  duct  proceeds  to  open  into  the  nose- 
chamber  below  the  inferior  turbinate  bone  (q,  Fig.  41,  p. 
133). 

Tears  are  constantly  being  secreted,  but  ordinarily  in 
such  quantity  as  to  be  drained  off  into  the  nose,  from 
which  they  flow  into  the  pharynx  and  are  swallowed. 
When  the  lachrymal  duct  is  stopped  up,  however,  their 

Of  what  parts  does  the  lachrymal  apparatus  consist?  Describe  the 
lachrymal  gland.  Where  do  its  ducts  open?  How  is  the  front  of  the 
eyeball  kept  moist?  Describe  the  arrangement  by  which  the  tears 
are  usually  carried  off. 


320 


THE  HUMAN  BODY. 


continual  presence  makes  itself  unpleasantly  felt,  and 
may  need  the  aid  of  a  surgeon  to  clear  the  passage.  In 
weeping  the  secretion  is  increased,  and  then  not  only  more 
of  it  enters  the  nose,  but  some  flows  down  the  cheeks. 
The  frequent  swallowing  movements  of  a  crying  child, 
sometimes  spoken  of  as  "  gulping  down  his  passion,"  are 
due  to  the  need  of  swallowing  the  extra  tears  which  reach 
the  pharynx. 


FIG.  88.— The  left  eyeball  in  horizontal  section  from  before  back.  1,  scle- 
rotic; 2,  junction  of  sclerotic'  and  cornea;  3,  cornea;  4,  5,  conjunctiva;  6,  pos- 
terior elastic  layer  of  cornea;  7,  ciliary  muscle;  10,  choroid;  11,  13,  diliary  pro- 
cesses; 14,  iris;  15,  retina';  l(i,  optic  nerve;  17.  artery  entering  retina  in  optic 
nerve;  18,~^ovea  centralis;  19,  region  wheie  sensory  part  of.  retina  ends:  22, 
suspensory  ligament ;  23  is  placed  in  the  canal  of  Petit,  and  the  line  from  25 
points  to  it;  24,  the  anterior  part  of  the  hyaloid  membrane;  26,  27,  28,  are  placed 
on  the  lejaeT  28  points  *o  the  line  of  attachment  around  it  of  the  suspensory  liga- 
ment; 29^  vitreous  humor;  3D,  anterior  chamber  of  aqueous  humor;  31,  poste- 
rior chamber  of  aqueous  humor. 

Why  do  tears  run  down  the  face  during  a  fit  of  weeping? 

Why  does  a  crying  child  make  frequent  swallowing  movements? 


THE  EYEBALL.  321 

The  Globe  of  the  Eye  is  on  the  whole  spheroidal,  but 
consists  of  segments  of  two  spheres  (see  Fig.  88),  a  portion 
of  a  sphere  of  smaller  radius  forming  its  anterior  transpar- 
ent part,  and  being  set  on  to  the  front  of  its  posterior 
segment,  which  is  part  of  a  larger  sphere.  In  general 
terms  it  may  be  described  as  consisting  of  three  coats  and 
three  refracting  media. 

The  outer  coat  1  and  3,  Fig.  88,  consists  of  the  sclerotic 
and  the  cornea,  the  latter  being  transparent  and  situated  in 
front ;  the  former  is  opaque  and  white  and  covers  the  back 
and  sides  of  the  globe  and  part  ol  the  front,  where  it  is 
seen  between  the  eyelids  as  the  white  of  the  eye.  Both  are 
tough  and  strong,  being  composed  of  dense  connective  tissue. 

The  second  coat  consists  of  the  choroid,  9,  10,  and  the 
iris,  14.  The  choroid  consists  mainly  of  blood-vessels  sup- 
ported by  loose  connective  tissue,  which  in  its  inner  layers 
contains  many  dark  brown  or  black  pigment  granules.* 
Towards  the  front  of  the  eyeball,  where  it  begins  to  dimin- 
ish in  diameter,  the  choroid  separates  from  the  sclerotic 
and  turns  in  to  form  the  iris,  or  that  colored  part  of  the 
eye  which  is  seen  through  the  cornea ;  in  the  centre  of  the 
iris  is  a  circular  aperture,  the  pupil,  through  which  light 
reaches  the  interior  of  the  eyeball. 

The  third  or  innermost  coat  of  the  eye,  the  retina,  15, 
is  its  essential  portion,  being  the  part  in  which  £he  light 
produces  those  changes  that  give  rise  to  nervous  impulses 
in  the  optic  nerve.  It  lines  the  posterior  half  of  the  eyeball. 

The  Microscopic  Structure  of  the  Retina  is  very  com- 

What  is  the  form  of  the  globe  of  the  eye?   Of  what  does  it  consist? 
Describe  the  outer  coat.     The  second  coat.     What  is  the  retina? 


*  In  pink-eyed  rabbits  and  in  the  pink-eyed  ladies  of  "  dime  museums"  this 
pigment  is  absent. 


322 


THE  HUMAN  BODY. 


plex  ;  although  but  -£$  inch  in  thickness  it  presents  ten  dis< 
tinct  layers. 


FIG.  89.— A  section  through  the  retina  from  its  anterior  or  inner  surface,  1 
in  contact  with  the  hyaloid  membr  ine,  to  its  outer,  10,  in  contact  with  the  cha 
roid.  1,  internal  limiting  membrane;  2,  nerve-fibre  layer;  3,  nerve-cell  layer;  4, 
inner  molecular  layer;  5,  inner  granular  layer;  6,  outer  molecular  layer;  7, 
outer  granular  layer;  8,  external  limiting  membrane;  9,  rod  and  cone  layer;  10", 
pigment-cell  layer. 

Beginning  (Fig.  89)  on  its  front  or  inner  side  we  find, 


THE  RETINA.  323 

first,  the  internal  limiting  membrane,  1,  a  thin  structure- 
less layer.  Next  comes  the  nerve-fibre  layer,  2,  formed  by 
radiating  fibres  of  the  optic  nerve ;  third,  the  nerve-cell 
layer,  3;  fourth,  the  inner  molecular  layer,  4,  consisting 
partly  of  very  fine  nerve-fibrils,  and  largely  of  connective 
tissue  ;  fifth,  the  inner  granular  layer,  5,  composed  of  nu- 
cleated cells,  with  a  small  amount  of  protoplasm  at  each 
end,  and  a  nucleolus.  These  granules,  or  at  any  rate  the 
majority  of  them,  have  an  inner  process  running  to  the  in- 
ner molecular  layer,  and  an  outer  running  to,  6,  the  outer 
molecular  layer,  which  is  thinner  than  the  inner.  Then 
comes,  seventh,  the  rod  and  cone  fibre  layer,  7,  or  outer 
granular  layer,  composed  of  thick  and  thin  fibres  on  each 
of  which  is  a  conspicuous  nucleus  with  a  nncleolus.  Next 
is  the  thin  external  limiting  membrane,  8,  perforated  by 
apertures  through  which  the  rods  and  cones,  9,  of  the 
ninth  layer  join  the  fibres  of  the  seventh.  Outside  of  all, 
next  the  choroid,  is  the  pigmentary  layer,  10.  The  nerve- 
fibres  are  believed  to  be  continuous  with  the  rods  and  cones. 
Light  entering  the  eye  passes  through  the  transparent  retina 
until  it  reaches  the  rods  and  cones  and  excites  these,  and 
they  stimulate  the  nerves. 

The  action  of  the  light  is  probably  in  the  first  instance 
chemical.  The  rods  are  stained  by  a  purple  substance, 
which  is  bleached  by  light  and  regenerated  in  the  dark.  In 
the  healthy  eye  the  purple  is  reproduced  nearly  as  fast  as  de- 
stroyed, by  the  pigment-cells  of  the  retina.  Parts  of  the  retina 
which  contain  none  of  this  visionpurple  can  see, but  they  may 
possess  uncolored  substances  which  are  changed  by  light. 

Describe  the  microscopic  structure  of  the  retina.  On  what  con. 
stituents  of  the  retina  does  light  first  act,  in  producing  a  sensation? 

With  what  are  the  rods  of  the  retina  stained?  How  is  the  pig- 
ment reproduced? 


324 


THE  HUMAN  BODY. 


The  Blind  Spot, — Where  the  optic  nerve  enters  the  re- 
tina it  forms  a  small  elevation  (Fig.  90),  from  which  nerve- 


FIG.  90.— The  right  retina  as  it  would  be  seen  if  the  front  part  of  the  eyeball 
with  the  lens  and  vitreous  humor  were  removed.  The  white  disc  to  the  right 
marks  the  entry  of  the  opiic  nerve  (blind  spot);  the  lines  radiating  from  this  are 
the  retinal  arteries  and  veins.  The  small  central  durk  patch  is  the  yellow  spot, 
the  region  of  mobt  acute  vision. 

fibres  radiate.  This  elevation  is  quite  blind,  because  it  pos- 
sesses neither  rods  nor  cones.  Its  blindness  may  be  readily 
demonstrated.  Close  the  left  eye  and  look  steadily  with  the 
right  at  the  cross  (Fig.  91),  holding  the  page  vertically  in 


FIG.  91. 

What  is  meant  by  the  "blind  spot"?    Describe  a  method  of 
demonstrating  its  blindness. 


THE  REFRACTING  MEDIA   OF  THE  EYE.        325 

front  of  the  face,  and  moving  it  alternately  from  and  towards 
you.  The  eye  must  all  the  time  be  kept  looking  fixedly  at 
the  cross.  When  the  book  is  about  ten  inches  from  the 
eye  the  white  disc  entirely  disappears  from  view:  its  image 
then  falls  on  the  part  of  the  retina  where  the  optic  nerve 
enters,  and  causes  no  visual  sensation. 

Light  consists  of  vibrations  in  an  ether  which  pervades 
space.  An  object  which  sets  up  no  waves  in  the  ether  does 
not  excite  the  visual  nervous  apparatus,  and  appears  black; 
an  object  which  sets  up  ethereal  vibrations  capable  of 
exciting  the  rods  and  cones  of  the  retina  appears  white 
or  colored  when  we  look  at  it.  The  ethereal  vibrations 
enter  the  eye  through  the  cornea,  pass  on  through  the 
pupil,  and  reach  and  stimulate  the  retina. 

The  Refracting  Media  of  the  Eye  are  three  in  number: 
(1)  the  aqueous  "humor ;  (2)  the  crystalline  lens ;  (3)  the 
vitteous  humor.  Their  relative  positions  are  shown  in  Fig. 
88.  These  media  act  like  a  convex  lens,  such  as  a  common 


FIG.  92. — Illustrating:  the  formation  behind  a  convex  lens  of  a  diminished 
and  inverted  image  of  an  object  placed  in  front  of  it. 

burning-glass,  and  bend  the  rays  of  light  which  pass  through 
them  (Fig.  92),  so  that  all  those  which  start  from  one  point 
of  an  external  object  meet  again  in  a,  focus  on  one  point  of 

What  is  light?    When  does  an  object  appear  black? 
Name  the  refracting  media  of  the  eye.     State  their  relative  posi- 
tion.    Describe  their  action. 


326  THE  HUMAN  BODY. 

the  retina.  In  this  way  a  small  and  inverted  image  of  the 
things  at  which  we  look  is  formed  on  the  retina,  and  stimu- 
lates its  rods  and  cones. 

Accommodation.— In  the  healthy  eyeball  the  crystalline 
lens  is  controlled  by  muscles  which  change  its  convexity, 
making  this  greater  when  we  look  at  near  objects,  and  less 
when  we  look  at  distant  objects.  When  the  lens  is  very 


FIG.  98.— Section  of  front  part  of  eyeball  showing  the  change  in  the  form 
of  the  lens  when  near  and  distant  objects  are  looked  at.  a,  c,  fc,  cornea;  A,  lens 
when  near  object  is  looked  at;  B,  lens  when  distant  object  is  looked  at. 

convex  we  cannot  see  a  distant  object  distinctly,  and  when 
it  is  less  convex  we  only  dimly  see  a  near  object.  For 
example,  standing  at  a  window  behind  a  lace  curtain  we 
can  look  at  the  curtain  and  see  its  threads  plainly,  but  while 
so  doing  we  only  see  indistinctly  houses  on  the  other  side 
of  the  street;  because  the  convexity  of  the  lens  is  then  such 
as  to  focus  light  from  the  near  object  on  the  retina,  and  not 
that  from  the  distant.  We  can,  however,  "look  at"  the 
houses  over  the  way  and  see  them  plainly;  but  then  we  no 
longer  see  the  curtain  distinctly,  because  the  lens  has  so 
changed  its  form  as  to  focus  light  from  the  far  object  on  the 

When  we  look  at  an  object,  what  is  formed  on  the  retina? 

How  is  the  form  of  the  crystalline  lens  controlled?  When  is  its 
convexity  greater?  Can  we  see  near  and  distant  objects  distinctly 
at  the  same  moment?  Illustrate. 


SHORT  SIGHT  AND  LONG  SIGHT. 


327 


retina,  instead  of  light  from  the  near.  The  power  of  chang* 
ing  the  form  of  the  lens  according  as  near  or  distant  objects 
are  looked  at  is  called  "accommodation." 

Short  Sight  and  Long  Sight. — In  the  normal  eye  the  range 
of  accommodation  is  very  great,  allowing  light  from  objects 
infinitely  distant  up  to 
that  proceeding  from 
those  only  about  eight 
inches  in  front  of  the  eye 
to  be  brought  to  a  focus 
on  the  retina.  In  the 
natural  healthy  eye  par- 
allel rays  of  light  meet  on 
the  retina  when  the  mus- 
cles controlling  the  crys- 
talline lens  are  at  rest  and 
the  lens  is  at  its  flattest 
(A,  Fig.  94).  Such  eyes 
are  emmetropic.  In  other 
eyes  the  eyeball  is  too 
long  from  before  back;  of 
in  the  resting  state  paral-  £$§  $'££*** 
lei  rays  meet  in  front  of  the  retina  (B).  Persons  with 
such  eyes  cannot  see  distant  objects  distinctly  without  the 
aid  of  diverging  (concave)  spectacles;  they  are  short-sighted 
or  myopic.  Or  the  eyeball  may  be  too  short  from  before 
back;  then,  in  its  resting  state,  parallel  rays  are  brought 

What  is  meant  by  the  "accommodation"  of  the  eyeball? 

Where  do  parallel  rays  of  light  which  have  entered  a  healthy  eye 
meet  in  a  focus?  Where  do  such  rays  meet  when  the  eyeball  is  too 
long  from  back  to  front?  What  is  the  result  as  regards  vision? 
What  form  of  spectacle  lenses  do  short-sighted  persons  require?  Ex- 
plain what  is  meant  by  a  hypermetropic  or  long-sighted  eye.  What 
sort  of  spectacles  do  long-sighted  persons  require? 


328  THE  HUMAN  BODY. 

to  a  focus  behind  the  retina  ( C).  To  see  even  distant  ob- 
jects, such  persons  must  therefore  use  muscular  effort  to 
increase  the  converging  power  of  the  lens;  and  when  objects 
are  near  they  cannot,  with  the  greatest  effort,  bring  the 
rays  proceeding  from  them  to  a  focus  soon  enough.  To 
get  distinct  retinal  images  of  near  objects,  they  therefore 
need  converging  (convex)  spectacles.  Such  e}'es  are  called 
hypermetropic,  or  in  common  language  long-lighted. 

Hygiene  of  the  Eyes.— The  healthy  eye  is  so  constructed 
that  when  its  muscles  are  at  rest  distinct  images  of  distant 
objects  are  focussed  on  the  retina.  To  see  near  objects 
muscular  effort  is  required;  hence  the  greater  fatigue  which 
follows  long  gazing  at  them. 

In  a  hyperme tropic  eye  more  effort  is  needed  to  see  near 
objects,  and  this  results  in  muscular  fatigue.  Hyper- 
metropic  persons  can  often  read  well  for  a  while,  but  then 
complain  that  they  can  no  longer  see  distinctly.  This  kind 
of  weak  sight  should  always  lead  to  examination  of  the 
e}res  by  an  oculist,  to  see  if  glasses  are  needed;  otherwise 
severe  neuralgic  pains  about  the  eyes  are  apt  to  come  on, 
and  the  overstrained  organ  may  be  permanently  injured. 

Children  sometimes  have  hypermetropic  eyes,  and  in 
that  case  should  be  at  once  provided  with  suitable  spec- 
tacles. In  old  age  another  kind  of  long-sightedness  (pres- 
byopia) is  common:  it  is  due  to  too  great  stiffness  of  the 
crystalline  lens,  which  does  not  become  convex  enough 
during  accommodation  to  focus  on  the  retina  the  images  of 
near  objects. 

Short-sighted  eyes  appear  to  be  more  common 
now  than  formerly,  especially  in  those  given  to  indoor 

Why  is  the  eye  apt  to  be  fatigued  by  the  continued  contempla- 
tion of  near  objects  ? 

How  does  the  hypermetropic  eye  differ  from  the  normal  in  the 
above  respect?  What  should  be  done  at  once  if  a  child  is  found  to 
have  hypermetropic  eyes?  What  is  presbyopia? 

In  what  classes  of  persons  is  myopia  most  frequent? 


HEARING. 


329 


pursuits.  Myopia  is  rare  among  those  who  cannot  read  or 
who  live  mainly  out  of  doors.  It  is  not  so  apt  to  lead  to 
permanent  injury  of  the  eye  as  hypermetropia,  but  the 
effort  to  see  distinctly  any  but  near  objects  is  apt  to  pro- 
duce headaches  and  other  symptoms  of  nervous  exhaus- 
tion. If  the  myopia  becomes  gradually  worse,  the  eyes 
should  be  rested  for  several  months. 

Hearing. — The  auditory  organ  (Fig.  95)  consists  of  three 
portions,  known  respectively  as  the  external  ear,  the  middle 


FIG.  95.— Semi-diagrammatic  section  through  the  right  ear.  M,  concha.  (?, 
external  auditory  meatus.  2'.  tympanic  or  drum  membrane.  P,  Tympanum, 
o,  oval  foramen,  r.  round  foramen.  Extending  from  7'to  o  is  seen  the  chain  of 
tympanic  bones.  R,  Eustachian  tube.  V,  B,  S,  bony  labyrinth:  F",  vestibule; 
B,  semicircular  canal ;  S,  cochlea.  6, 1,  I',  membranous  semicircular  canal 
and  vestibule.  A,  auditory  nerve  dividing  into  branches  for  vestibule,  semi- 
circular canal,  and  cochea. 

ear  or  tympanum,  and  the  internal  ear  or  labyrinth ;  of 
these  the  latter  is  the  essential  one,  containing  the  ends  of 
the  auditory  nerve-fibres. 

What  is  apt  to  result  from  short  sight? 
Of  what  does  the  auditory  organ  consist? 


330 


THE  HUMAN  BODY. 


The  External  Ear  consists  of  the  expansion,  Mt  seen  on 
the  exterior  of  the  head,  called  the  concha,  and  a  passage 
leading  in  from  it,  the  external  auditory  meatus,  G.  Thig 
passage  is  closed  at  its  inner  end  by  the  tympanic  or  drum 
membrane,  T.  It  is  lined  by  a  prolongation  of  the  skin, 
through  which  numerous  small  glands,  secreting  the  wax 
of  the  ear,  open. 

The  Tympanum, or  drum  chamber  of  the  ear  (Fig.  96  and 

P,  Fig.  95),  is  an 
irregular  cavity  in 
the  temporal  bone, 
closed  externally  by 
the  drum  membrane. 
From  its  inner  side 
the  EustacMan  tube 
(R,  Fig.  95)  pro- 
ceeds and  opens 
into  the  pharynx. 
This  tube  allows  air 
fsom  the  throat  to 
enter  the  tympanum, 
and  serves  to  keep 

FIG.  96.— The  tympanic  cavity  and  its  bones,  con-  pnivil  f]1P  nfmrxsnTipr 

siderably  magnified.     G,  the  inner  end  of  the  ex-  UiUtl 

ternal  auditory  meatus,  closed  internally  by  the  \n    -nvnccnvn    rm    oor»"U 

conical  tympanic  membrane:  I/,  the  malleus,  or  1 

hammer-bone;  H,  the  incus,  or  anvil-bone;  S,  the  -i^      r&      L-I  n      ,qw 

stapes,  or  stirrup-bone.  Side     01      the     drum 

membrane.  Three  small  bones  (Fig.  96)  stretch  across 
the  tympanic  cavity  from  the  drum  membrane  to  the  laby- 
rinth ;  they  transmit  the  vibrations  .of  the  membrane, 
produced  by  sound-waves  ,in  the  air,  to  the  liquid  of  the 

Describe  the  external  ear. 

What  is  the  tympanum?  The  Eustaehian  tube?  What  is  the  use 
of  the  Eustaehian  tube?  What  bones  lie  in  the  tympanum?  What 
is  their  function? 


TOUGH.  331 

labyrinth.     The  outmost  bone  is  the  malleus  ;  the  inmost, 
the  stapes  j  and  the  middle  bone,  the  incus. 

The  Internal  Ear,  or  Labyrinth,  consists  primarily  of 
chambers  and  tubes  hollowed  out  in  the  temporal  bone. 
The  middle  chamber,  called  the  vestibule  ( V,  Fig.  95),  has 
an  opening,  the  oval  foramen,  o,  in  its  outer  side,  into  which 
the  inner  end  of  the  stapes,  or  stirrup-bone,  fits.  Behind, 
the  vestibule  opens  into  three  semicircular  canals,  one  of 
which  is  shown  at  B,  Fig.  95;  and  in  front  into  a  spirally 
coiled  tube,  S,  the  cochlea.  In  these  bony  chambers  and 
tubes  lie  membranous  chambers  and  tubes,  in  which  the 
fibres  @f  the  auditory  nerve  (A,  Fig.  95)  end.  All  the 
labyrinth  chamber  outside  these  membranous  parts  is 
occupied  by  a  watery  liquid,  known  as  perilymph;  the 
membranous  chambers  are  filled  with  a  similar  liquid,  the 
endolymph. 

When  sound-waves  of  the  air  make  the  tympanic  mem- 
brane vibrate,  it  shakes  the  tympanic  bones;  the  stapes 
then  shakes  the  liquids  in  the  labyrinth,  and  sets  up  vibra- 
tions in  them,  which  excite  the  endings  of  the  auditory 
nerve.  The  stimulated  auditory  nerve  then  conveys  a 
nervous  impulse  to  the  brain-centre  of  hearing  and  excites 
it,  and  a  sensation  of  sound  results-. 

Touch,  or  the  Pressure  Sense. — Many  sensory  nerves  end 
in  the  skin,  and  through  it  we  get  several  kinds  of  sensa- 


Of  what  does  the  internal  ear  primarily  consist?  What  is  the 
vestibule? 

What  is  found  on  the  outer  side  of  the  vestibule? 

Into  what  does  the  vestibule  open  behind?  In  front?  What  lie 
in  the  bony  cavities  of  the  labyrinth?  What  is  the  perilymph?  The 
endolymph? 

What  happens  when  sound-waves  set  the  tympanic  membrane  in 
vibration? 


332  THE  HUMAN  BODY. 

tion;  touch  proper,  heat  and  cold,  and  pain ;  and  we  can 
with  more  or  less  accuracy  localize  them  on  the  surface  of 
the  body.  The  interior  of  the  mouth  possesses  also  these 
sensibilities.  Through  touch  proper  we  recognize  pressure 
or  traction  exerted  on  the  skin,  and  the  force  of  the  pres- 
sure; the  softness  or  hardness,  roughness  or  smoothness,  of 
the  body  producing  it;  and  the  form  of  this,  when  not  too 
large  to  be  felt  all  over. 

The  delicacy  of  the  tactile  sense  varies  on  different  parts 
of  the  skin;  it  is  greatest  on  the  forehead  and  temples, 
where  a  weight  of  yf^  of  a  grain  can  be  felt. 

The  Localization  of  Skin  Sensations. — When  the  eyes  are 
closed  and  a  point  of  the  skin  is  touched  we  can  with  some 
accuracy  indicate  the  region  stimulated;  although  tactile 
feelings  are  alike  in  general  characters,  they  differ  in  some- 
thing (local  sign)  besides  intensity  by  which  we  can  distin- 
guish them  as  originated  on  different  parts  of  the  skin. 
The  accuracy  of  the  localizing  power  varies  widely  in  dif- 
ferent skin  regions,  and  is  measured  by  observing  the  least 
distance  which  must  separate  two  objects  (as  the  blunted 
points  of  a  pair  of  compasses)  in  order  that  they  may  be 
felt  as  two.  The  following  table  illustrates  some  of  the 
differences  observed: 

Tongue-tip 04  inch 

Palm  side  of  last  phalanx  of  finger 08     " 

Red  part  of  lips 16     " 

Tip  of  nose 24     " 

Back  of  second  phalanx  of  finger 44     " 

Heel 88     " 

What  sensations  do  we  get  through  the  skin?  Name  another  part 
of  the  body  which  also  gives  rise  to  these  sensations.  What  do  we 
recognize  by  means  of  the  sense  of  touch? 

Where  is  the  tactile  sense  most  acute? 

What  is.meant  by  the  localization  of  skin  sensations?  Does  the  ac- 
curacy of  localization  differ  in  different  regions  of  the  skin?  Illustrate. 


SMELL.  333 

Back  of  hand 1.23  inches 

Forearm 158       " 

Sternum 1.76       " 

Back  of  neck 2.11       " 

Middle  of  back 2. 64 

The  Temperature  Senses.— By  these  is  meant  our  faculty 
of  perceiving  cold  and  warmth;  and,  with  the  help  of  these 
sensations,  of  perceiving  temperature  differences  in  external 
objects.  The  organs  are  the  skin,  the  mucous  mem- 
brane of  mouth,  pharynx,  and  gullet,  and  of  the  entry  of 
the  nose.  Burning  the  skin  will  cause  pain,  but  not  a  true 
temperature  sensation,  which  is  quite  as  different  from 
pain  as  is  touch. 

Smell. — The  olfactory  organ  consists  of  the  mucous 
membrane  of  the  upper  parts  of  the  nasal  cavities;  in  it  the 
endings  of  the  olfactory  nerves  are  spread.  It  covers  the 
upper  and  lower  turbinate  bones  (o,  p,  Fig.  41)  (which  are 
expansions  of  the  ethmoid  on  the  outer  wall  of  the  nostril- 
chamber),  the  opposite  part  of  the  partition  between  -the 
nares,  and  that  part  of  the  roof  of  the  nose  (n,  Fig.  41) 
which  separates  it  from  the  cranial  cavity. 

Odorous  Substances,  the  stimuli  of  the  olfactory  apparatus, 
are  always  gaseous.  They  frequently  act  powerfully  when 
present  in  very  small  quantity.  A  grain  or  two  of  musk 
kept  in  a  room  will  give  the  air  in  it  an  odor  for  years,  and 
yet  at  the  end  will  hardly  have  diminished  in  weight,  so 
infinitesimal  is  the  quantity  given  off  from  it  to  the  air 
and  able  to  excite  the  sense  of  smell.  While  some  gases  or 

What  is  the  temperature  sense?     What  are  its  organs? 

Of  what  does  the  olfactory  organ  consist? 

In  what  point  do  all  odorous  substances  agree?  Illustrate  the 
efficiency,  so  far  as  producing  smell  sensations  is  concerned,  of  a 
very  small  quantity  of  an  odorous  substance.  Do  all  gases  stimulate 
the  olfactory  apparatus? 


334  THE  HUMAN  BODY. 

vapors  have  this  powerful  influence  upon   the   olfactory 
organ,  others,  as  pure  air,  do  not  stimulate  it  at  all. 

Taste. — The  organ  of  taste  is  the  mucous  membrane  on 
the  upper  side  of  the  tongue,  and  possibly  on  other  parts  of 
the  boundary  of  the  mouth  cavity.  The  mucous  membrane 
of  the  tongue  presents  innumerable  elevations  or  papillae 
(Fig.  46)  of  three  kinds  (p.  139).  The  filiform  papillae  are 
organs  of  touch,  for  the  tongue  has  the  sense  of  touch  as 
well  as  of  taste.  The  circumvallate  and  fungiform  papillae 
contain  the  endings  of  branches  of  the  glosso-pharyngeal 
and  trigeminal  nerves  (pp.  292,  203),  which,  when  excited 
by  sapid  bodies,  stimulate  the  taste-centres  in  the  brain. 

Many  so-called  tastes  (flavors)  are  really  smells;  odorif- 
erous particles  of  substances  which  are  being  eaten  reach 
the  nose  through  the  posterior  nares  and  arouse  smell  sen- 
sations which,  since  they  accompany  the  presence  of  ob- 
jects in  the  mouth,  we  take  for  tastes.  Such  is  the  case 
with  most  spices;  when  the  nasal  chambers  are  blocked  or 
inflamed  by  a  cold  in  the  head,  or  closed  by  pinching  the 
nose,  the  so-called  "  taste"  of  spices  is  not  perceived  when 
they  are  eaten;  all  that  is  felt  when  cinnamon,  e.g.,  is 
chewed  under  such  circumstances  is  a  certain  pungency 
due  to  its  stimulation  of  nerves  of  common  sensation  in  the 
tongue.  This  fact  is  sometimes  taken  advantage  of  in  the 
practice  of  domestic  medicine  when  a  nauseous  dose,  as 
rhubarb,  is  to  be  given  to  a  child. 

What  is  the  organ  of  taste?  What  is  found  on  the  mucous  mem- 
brane of  the  tongue?  What  papillae  are  concerned  in  the  tactile  sen- 
sibility of  the  tongue?  In  the  gustatory  ?  What  nerves  supply  the 
taste-papillse? 

What  are  many  so-called  tastes?    Illustrate. 


CHAPTER  XXII. 
VOICE  AND  SPEECH. 

Voice  consists  of  sounds  produced  by  the  vibrations  of 
two  elastic  bands  called  the  vocal  cords.  These  cords  lie 
in  the  larynx,  which  is  situated  between  the  pharynx  and 
the  windpipe,  and  is  a  portion  of  the  passage  conveying  air 
to  the  lungs  specially  modified  to  form  a  voice-organ. 

The  vocal  cords  project  into  the  larynx  so  that  but  a 
narrow  slit,  called  the  glottis,  is  left  between  them.  When 
the  vocal  cords  are  put  in  a  certain  position  air  driven 
through  the  glottis  sets  them  vibrating  and  they  give 
origin  to  sounds.  The  stronger  the  blast  the  louder  the 
voice. 

The  pitch  of  the  voice  is  primarily  dependent  on  the  size 
of  the  larynx.  The  larger  it  is,  or  what  comes  to  the  same 
thing,  the  longer  the  vocal  cords  are,  the  lower  is  the  pitch 
of  the  voice.  In  children,  therefore,  the  voice  is  shrill; 
and,  as  the  female  larynx  is  usually  smaller  than  the  male, 
a  woman's  voice  is  usually  higher  pitched  than  a  man's. 
About  sixteen  or  seventeen  years  of  age  a  boy's  larynx 
grows  very  fast,  and  his  voice  "breaks,"  becoming  about 
an  octave  deeper  in  tone. 

How  is  voice  produced?  Where  do  the  vocal  cords  lie?  Where 
is  the  larynx  situated? 

What  is  the  glottis?  When  do  the  vocal  cords  give  origin  to 
sounds?  On  what  does  the  loudness  of  the  voice  depend? 

How  does  the  size  of  larynx  influence  the  pitch  of  the  voice? 
Why  is  a  woman's  voice  commonly  higher  pitched  than  a  man's? 
Why  does  a  youth's  voice  break? 


336  THE  HUMAN  BODY. 

While  every  one's  voice  has  a  certain  natural  pitch  which 
leads  us  to  call  it  soprano,  tenor,  bass,  and  so  forth,  this 
pitch  can  be  modified  within  limits,  so  that  we  each  can 
sing  a  number  of  notes.  This  variety  is  due  to  the  action 
of  muscles  in  the  larynx  which  alter  the  tension  of  the 
vocal  cords;  the  more  tightly  these  are  stretched,  other 
things  being  equal,  the  higher  pitched  is  the  tone  which 
they  emit. 

Speech. — The  vocal  cords  alone  would  produce  but  feeble 
sounds.  If  a  fiddle-string  be  attached  to  a  hook  on  the 
ceiling  and  stretched  by  hanging  a  heavy  weight  on  its 
lower  end,  we  can  get  tones  out  of  it  when  it  is  plucked 
•or  bowed;  but  the  tones  are  feeble  and  deficient  in  charac- 
ter and  fullness.  In  the  violin  the  strings  are  attached  to  a 
hollow  wooden  box,  and  when  the  string  is  set  in  move- 
ment it  causes  the  wood  to  vibrate,  and  this,  in  turn,  the  air 
contained  in  the  cavity  of  the  instrument;  in  this  way  the 
tone  is  intensified,  and  altered  and  much  improved  in 
quality.  The  air  in  the  pharynx,  mouth,  and  nose  an- 
swers pretty  much  to  that  in  the  hollow  of  the  violin;  those 
cavities  together  form  a  resonance-chamber,  and  when  the 
vocal  cords  vibrate  they  set  this  air  in  vibration  also,  and 
so  the  sound  is  made  louder  and  is  altered  in  character. 
By  movements  of  throat,  soft  palate,  tongue,  cheeks,  and 
lips,  the  size  and  form  of  the  sounding'chamber  are  varied, 
and  with  them  the  tone  of  voice;  by  movements  of  tongue, 
lips,  and  palate,  the  air-current,  and  therefore  the  sound, 
is  interrupted  from  time  to  time;  on  other  occasions  the 

How  is  it  that  we  can  sing  a  number  of  notes  of  different  pitch? 

Why  is  a  hollow  wooden  box  an  essential  part  of  a  violin?  How 
do  the  throat  and  mouth  cavities  influence  the  loudness  and  quality 
of  the  voice?  How  do  tongue,  lips,  and  cheeks  co-operate  in  con- 
verting voice  into  speech? 


THE  LARYNX.  337 

air  is  forced  through  a  narrow  passage  in  the  mouth,  giving 
rise  to  new  sounds  added  on  to  those  originated  by  the  vocal 
cords.  In  such  manners  the  primitive  feeble  monotonous 
tone  due  to  the  vocal  cords  is  reinforced  and  altered  in 
various  ways  in  throat  and  mouth,  and  voice  is  developed 
into  articulate  speech. 

The  Larynx  consists  of  a  framework  of  nine  cartilages, 


FIG.  97.— The  more  important  cartilages  of  the  larynx  from  behind,  t,  thy- 
roid; Cs,  its  superior,  and  6V,  its  inferior,  horn  of  the  right  side;  *#,  cricoid 
cartilage;  t,  arytenoid  cartilage;  Pv,  the  corner  to  which  the  posterior  end  of  a 
vocal  cord  is  attached;  P»i,  corner  on  which  the  muscles  which  approximate  or 
separate  the  vocal  cords  are  inserted;  cu,  cartilage  of  Santorini. 

movabty  articulated  together,  and  having  muscles  attached 
to  them  by  whose  contractions  their  relative  positions  are 
altered;  the  cartilages  surround  a  tube,  continuous  below 
with  the  windpipe,  and  lined  by  mucous  membrane.  At 
one  level  in  the  laryngeal  tube  the  vocal  cords  project  and, 

Of  what  does  the  laryngeal   framework  consist?    What  do  the 
Cartilages  of  the  larynx  surround?    How  is  the  glottis  formed? 


338  THE  HUMAN  BODY. 

pushing  out  the  mucous  membrane,  leave  for  the  passage 
of  air  only  the  narrow  slit  of  the  glottis,  above  mentioned. 

The  largest  cartilage  of  the  larynx  (t,  Fig.  97)  is  the 
thyroid.  It  is  placed  in  front  and  consists  of  right  and 
left  halves  which  meet  at  an  angle  in  front,  but  separate 
behind  so  as  to  enclose  a  V-shaped  space.  The  front  of 
the  thyroid  cartilage  causes  the  prominence  in  the  neck 
known  as  Adam's  apple.  The  epiglottis,  not  represented 
in  the  figure,  is  attached  to  the  top  of  the  thyroid  cartilage 
and  overhangs  the  entry  from  pharynx  to  larynx.  It  may 
be  seen,  covered  by  mucous  membrane,  projecting  at  the 
root  of  the  tongue,  if  that  organ  be  pushed  down,  while 
the  mouth  is  held  open  before  a  mirror.  *  It  is  represented 
as  seen  from  behind  at  a,  Fig.  98.  The  cricoid  cartilage 
(**,  Fig.  97)  has  the  form  of  a  signet-ring,  with  its  broad 
part  turned  towards  the  back  of  the  throat,  and  placed  in 
the  lower  part  of  the  opening  between  the  halves  of  the 
thyroid.  The  two  arytenoid  cartilages  ( f ,  Fig.  97)  are 
placed  on  the  top  of  the  wide  posterior  part  of  the  cricoid; 
each  is  pyramidal  in  form.  The  remaining  laryngeal  car- 
tilages are  of  less  importance. 

The  Vocal  Cords,  which  are  rather  projecting  pads  of 
elastic  tissue  than  cords  in  the  ordinary  sense  of  the  word, 
proceed,  one  from  each  arytenoid  cartilage  behind,  to 
the  angle  where  the  halves  of  the  thyroid  meet  in  front. 
In  quiet  breathing  the  interval  (glottis)  between  them  (c, 


Describe  the  position  and  form  of  the  thyroid  cartilage.  What 
causes  "  Adam's  apple"?  What  is  the  epiglottis?  How  may  you  see 
it  in  your  own  throat?  Describe  th«  cricoid  cartilage.  What  carti- 
lages are  set  on  top  of  the  cricoid?  What  is  their  form  ? 

Between  what  points  are  the  vocal  cords  stretched?  Under  what 
circumstances  does  air  driven  through  the  glottis  not  sot  them  vi- 
brating? 


MUSCLES  OF  THE  LARYNX. 


339 


Fig.  98)  is  narrow  in  front  and  wider  behind:  under  such 
circumstances  air  driven  through  the  opening  does  not  set 
the  margins  of  the  cords  in  vibration,  and  no  sound  is  pro- 
duced. 

The  Muscles  of  the  Larynx,    The  laryngeal  muscles 


FIG.  98.— The  larynx  viewed  from  its  pharyngeal  opening.  The  back  wall  of 
the  pharynx  has  been  divided  and  its  edges  (11)  turned  aside.  1,  body  of  hyoid; 
2,  its  small,  and  3,  its  great,  horns;  4,  upper  and  lower  horns  of  thyroid  car- 
tilage; 5,  mucous  membrane  of  front  of  pharynx,  covering  the  back  of  the  cri- 
coid  cartilage;  6,  upper  end  of  gullet;  7,  windpipe,  lying  in  front  of  the  gullet; 
8,  eminence  caused  by  cartilage  of  Santorini:  9,  eminence  caused  by  cartilage  of 
Wrisberg;  both  lie  in,  10,  the  aryteno-epiglottidean  fold  of  mucous  membrane, 
surrounding  the  opening  (aditus  laryngis)  from  pharynx  to  larynx.  «,  project- 
ing tip  of  epiglottis;  c,  the  glottis,  the  lines  leading  from  the  letter-point  to  the 
free  vibrating  edges  of  the  vocal  cords.  &',  the  ventricles  of  the  larynx:  their 
upper  cd~cs,  marking  them  off  from  the  eminences  6.  are  the  false  vocal  cords. 


340  THE  HUMAN  BODY. 

are  numerous,  and  are  arrange'd — (1)  to  pull  the  arytenoid 
cartilages  towards  one  another  and  so  narrow  the  glottis 
behind;  then  air  forced  through  the  narrowed  slit  sets  the 
cords  vibrating  and  produces  voice.  (2)  To  increase  the 
distance  between  the  arytenoid  cartilages  behind  and  the 
thyroid  in  front:  as  the  vocal  cords  are  attached  to  both, 
this  action  stretches  and  tightens  them,  and  so  raises  the 
pitch  of  the  voice.  (3)  To  pull  the  front  of  the  thyroid 
cartilage  nearer  the  arytenoids  and  so  slacken  the  cords  and 
lower  the  pitch  of  the  voice.  (4)  To  separate  the  arytenoid 
cartilages,  and  with  them  the  vocal  cords,  and  thus  widen 
the  glottis  and  allow  air  to  pass  through  it  without  pro- 
ducing voice. 

The  Range  of  the  Human  Voice  from  the  lowest  note 
(/"of  the  unaccented  octave)  of  an  ordinary  bass  to  the 
highest  note  (g  on  the  thrice-accented  octave)  of  a  fairly 
good  soprano  is  about  three  octaves:  the  former  note  is 
produced  by  176  vibrations  per  second,  the  latter  by  1584. 
Celebrated  singers  of  course  go  beyond  this  limit  in  each 
direction:  bassos  have  been  known  to  take  a  on  the  great 
octave  (110  vibrations  per  second),  and  Mozart,  at  Parma, 
heard  a  soprano  sing  a  note  of  the  extraordinarily  high  pitch 
c  on  the  fifth  accented  octave  (4224  vibrations  per  second). 

Vowels  are  musical  tones  produced  in  the  larynx  and 
modified  by  resonance  of  the  air  in  the  pharynx  and  mouth. 
To  get  the  broad,  a  sounds,  as  ah,  the  mouth  is  widely 
opened  and  the  lips  drawn  back;  to  get  such  vowels  as 


State  the  uses  of  the  muscles  of  the  larynx. 

What  is  the  ordinary  range  of  the  human  voice?  What  notes 
have  celebrated  singers  taken  beyond  the  ordinary  highest  and  lowest 
limits? 

What  are  vowels?  Illustrate  the  influence  of  the  shape  given  to 
the  mouth-cavity  in  the  production  of  different  vowels, 


VOWELS  AND   CONSONANTS. 

'  nc^; 

.,      ^v 

oo  (moor)  the  lips  are  protruded  and  th< 
lengthened.  The  change  in  the  form  of  th< 
be  noticed  by  pronouncing  consecutively  the  vowel-sounds 
ah,  eh}  ee,  oh,  oo.  The  English  i  (as  in  spire)  is  a  diph- 
thong, consisting  of  a  (pad)  followed  by  e  (feet),  as  may  be 
readily  found  on  attempting  to  sing  a  sustained  note  to  the 
sound  I. 

Semivowels. — In  uttering  true  vowel-sounds  the  soft 
palate  is  raised  so  as  to  cut  off  the  air  in  the  nose,  which 
then  does  not  take  part  in  the  resonance.  For  some  other 
sounds  (the  semivowels  or  resonant s)  the  initial  step  is,  as 
in  the  case  of  the  true  vowels,  the  production  of  a  laryngeal 
tone;  but  the  soft  palate  is  not  raised,  and  the  mouth-exit 
is  more  or  less  closed  by  the  lips  or  the  tongue;  hence  the 
blast  partly  issues  through  the  nose,  and  the  air  there  takes 
part  in  the  vibrations  and  gives  them  a  special  character; 
this  is  the  caso  with  m,  n,  and  ng. 

Consonants  are  sounds  produced  not  mainly  by  the  vocal 
cords,  but  by  modifications  of  the  expiratory  blast  on  its 
way  through  the  mouth.  The  current  may  be  interrupted 
and  the  sound  changed  by  the  lips  (labials,  as  p  and  b)\ 
or,  at  or  near  the  teeth,  by  the  tip  of  the  tongue  (dentals, 
as  t  and  d) ;  or,  in  the  throat,  by  the  root  of  the  tongue 
and  the  soft  palate  (gutturals,  as  k  and  g). 

Consonatfts  may  also  be  classified  by  the  kind  of  move- 
ment which  gives  rise  to  them.  In  explosives  an  interrup- 
tion to  the  air-current  is  suddenly  interposed  or  removed 
(p,  b,  t,  d,  Tc,  g).  Other  consonants  are  continuous  (/*, 
s,  r)  and  may  be  divided  into  (1)  aspirates,  when  the  air 

Is  the  long  i  of  English  a  true  vowel  ? 

What  is  meant  by  the  semivowels  ? 

What  are  consonants  ?    How  mav  they  be  classified  T 


342  THE  HUMAN  BODY- 

IS  made  to  rush  through  a  narrow  aperture,  as,  for  ex- 
ample, between  the  lips  (f)  or  the  teeth  (s)  or  the  tongue 
and  the  palate  (sh)  or  the  tongue  and  the  teeth  (th); 
(2)  resonants  or  semivowels;  (3)  vibratories,  the  different 
forms  of  r,  due  to  vibrations  of  parts  bounding  a  constric- 
tion put  in  the  way  of  the  air-current  on  its  passage. 


CHAPTER  XXIII. 

THE  ACTION  OF  ALCOHOL   AND   OTHER  STIMULANTS 
AND  NARCOTICS  UPON  THE  HUMAN  BODY. 

Introductory. — We  have  already  seen  (p.  121)  that  alcohol 
is  not  to  be  regarded  as  either  a  tissue-forming  or  a  force- 
giving  food. 

By  causing  a  transference  of  heat  from  internal  parts  to 
the  skin,  in  which  the  main  organs  of  the  temperature- 
sense  (p.  333)  are  located,  it  produces  a  temporary  feeling 
that  the  body  is  warmer;  but  the,  final  result  is  a  loss  of 
animal  heat  to  the  air,  and  a  decrease  of  the  temperature  of 
the  body  as  a  whole.  Experiments  made  on  men  under 
military  regimen  and  discipline  have  proved  that  alcohol 
does  not  increase  the  power  of  sustained  muscular  work, 
though  it  may  for  a  brief  time  stimulate  to  unhealthy 
activity.  The  relative  amount  of  energy  liberated  in  the 
body  for  its  own  use  may  be  very  fairly  calculated  by  com- 
paring the  amount  of  oxygen  absorbed  by  the  lungs  on  one 
day  with  the  amount  absorbed  on  another.  We  have  learned 
that  on  the  days  when  alcohol  is  taken  the  oxygen  absorbed 
is  not  increased.  Alcohol  seizes  some  of  the  oxygen  which 
the  foods  and  tissues  would  have  utilized  in  its  absence ; 
and  what  it  takes  they  lose.  Most  authorities  even  main- 
tain that  alcohol  prevents  oxidation,  and  therefore  tissue 

How  does  alcohol  make  one  feel  warmer?  What  is  the  result? 
What  have  experiments  on  soldiers  shown  as  to  the  effect  of 
alcohol  on  muscular  work?  How  is  the  absorption  of  oxygen 
affected  on  days  when  alcohol  is  taken?  What  does  alcohol  do  with 
some  of  the  oxygen?  Why  do  some  authorities  believe  that  alcohol 
directly  checks  tissue  activity? 

343 


344  THE  HUMAN  BODY. 

activity,  indirectly  as  well  as  directly;  these  experimenters 
find  that  it  not  only  takes  oxygen  from  the  tissues,  but 
so  influences  them  as  to  diminish  their  power  of  using 
what  it  leaves.  We  may  conclude  that  under  ordinary 
circumstances  alcohol  is  of  no  use  as  an  energy-yielding 
food;  although,  since  it  is  oxidized  in  the  body,  it  would 
act  as  a  real  food  to  a  starving  man;  or  to  a  very  sick  per- 
son who  might  be  unable  for  the  moment  to  absorb  and 
digest  other  substances. 

As  regards  tissue-formation,  alcohol  cannot  build  up 
proteid  material,  since  it  contains  no  nitrogen;  and  proteid 
material  constitutes  the  essential  part  of  muscular,  gland- 
ular, and  nervous  tissues.  There  is  even  some  evidence  that 
alcohol  leads  to  excessive  waste  of  such  tissues :  several 
competent  observers  have  found  that  its  use  increases  the 
amount  of  nitrogen  waste  excreted  from  the  body.  The 
only  tissues  whose  formation  alcohol  seems  sometimes  to 
increase  are  fatty  and  connective  tissues;  and  we  shall  pres- 
ently learn  that  in  most  cases  the  superabundance  of  these 
tissues  is  deposited  in  places  where  it  does  harm. 

The  study  of  alcohol  as  an  article  of  diet  leads  therefore 
to  the  result  that  (though  a  physician  may  find  it  useful  as 
a  medicine  in  a  crisis  of  disease  when  the  system  needs 
urging  to  make  a  special  effort)  it  cannot  fairly  be  regarded 
as  a  food  when  taken  by  persons  in  good  health  and  properly 
nourished. 

The  whip  applied  to  a  horse  will  arouse  him  to  call  on 

What  general  conclusions  may  be  reached  as  to  the  value  of  alco- 
hol as  a  food? 

What  relation  has  alcohol  to  the  formation  and  waste  of  proteid 
tissues?  Of  fatty  and  connective  tissues? 

When  may  a  physician  find  alcohol  a  useful  medicine? 

Illustrate  the  action  of  alcohol  on  the  body  by  comparison  with  a 
whip  used  on  a  horse. 


ALCOHOL.  345 

his  reserve  force,  and  perhaps  carry  himself  and  his  rider 
safely  past  some  point  of  special  danger;  but  it  does  not  in 
any  way  nourish  the  horse.  As  regards  the  healthy  human 
body  alcohol  may  be  compared  to  a  whip:  an  amount  of  it 
not  sufficient  to  cause  drunken  sleep,  temporarily  excites 
various  organs;  but  the  consequence  is  subsequent  greater 
exhaustion. 

So  far  we  have  learned  that  alcohol  as  a  regular  article 
of  diet  is,  at  least,  useless.  Were  that  all,  we  might  regret 
the  annual  waste  of  corn,  barley,  wheat,  and  fruits  in  its 
production;  and  think  the  man  foolish  who  spent  his 
money  on  it.  In  such  case  the  matter  would  be  one  for 
moralists  and  political  economists  to  deal  with,  and  phy- 
siologists and  students  of  hygiene  might  leave  it  alone. 
Unfortunately,  alcoholic  drinks  are  not  merely  useless  but 
positively  hurtful,  when  taken  regularly,  even  in  what  is 
usually  called  moderation.  Alcohol  has  probably  caused 
in  the  past,  and  is  certainly  causing  at  present  in  civilized 
nations,  more  disease  and  death  than  either  bad  drainage, 
bad  ventilation,  overcrowding,  deficient  food,  overwork,  or 
any  other  of  the  conditions  prejudicial  to  health  concern- 
ing which  Physiology  and  Hygiene  warn  us.  The  moral 
degradation  and  the  physical  condition  of  the  drunkard 
speak  for  themselves;  it  is  therefore  the  more  insidious 
consequences  of  alcohol-drinking  that  we  shall  mainly 
describe. 

Alcohol,  when  pure,  is  a  transparent  colorless  liquid, 
containing  the  elements  carbon,  hydrogen,  and  oxygen 
(C2H60);  it  is  lighter  than  water,  arid  boils  at  a  con- 

Wliat  substances  are  wasted  that  alcohol  may  be  produced? 
Compare  the  injury  to  health  resulting  from  bad  drainage,  etc. 
with  that  produced  by  alcohol. 
Describe  pure  alcohol. 


346  THE  I1UMAK  BODY. 

siderablj  lower  temperature;  is  highly  inflammable,  burn- 
ing with  a  bluish  flume;  and  is  the  essential  constituent  of 
all  fermented  liquors  in  common  use. 

Alcoholic  Beverages  include  (1)  malt  liquors,  as  beer,  ale, 
stout,  and  porter;  (xJ)  cider  and  perry;  (3)  wines,  as  claret, 
sherry,  port,  champagne,  and  catawba;  (4)  distilled  spirits, 
as  brandy,  rum,  and  whiskey;  and  their  compounds,  as  gin, 
cherry  brandy,  pineapple  rum,  and  so  forth;  (5)  liqueurs, 
made  by  adding  various  flavoring  essences  to  different  kinds 
of  spirits.  All  contain  alcohol  in  greater  or  less  propor- 
tion, varying  from  over  70  volumes  in  the  100  in  some 
kinds  of  rum  to  less  than  2  in  the  100  in  "small"  beer. 

The  Direct  Physiological  Action  of  Pure  Alcohol. — Pure 
alcohol  is  a  very  expensive  substance,  mainly  employed  in 
chemical  experiments  and  in  the  manufacture  of  certain 
perfumes  and  essences.  However,  some  clues  to  the  ac- 
tion of  diluted  alcohol  on  the  body  may  be  obtained  by  a 
study  of  its  action  in  the  concentrated  form. 

Strong  alcohol  having  a  great  tendency  to  combine  with 
water,  rapidly  extracts  that  substance  from  any  animal  organ 
placed  in  contact  with  it;  as  is  shown  by  the  hardening 
and  shrivelling  of  museum  specimens  placed  in  it. 

Added  to  raw  white  of  egg  it  coagulates  it,  much  as  if  the 
egg  had  been  boiled:  added  to  fresh  blood  it  acts  in  a  simi- 
lar manner,  coagulating  the  serum  albumen  as  heat  does 
(p.  183). 

Pure  alcohol  placed  on  the  skin  evaporates  very  rapidly, 
and  in  so  doing  abstracts  heat  (p.  274,  note),  producing  a 

Of  what  is  alcohol  an  essential  constituent? 

Classify  and  name  common  alcoholic  beverages.  Within  what 
limits  does  the  quantity  of  alcohol  in  them  vary? 

For  what  purposes  is  pure  alcohol  mainly  used?  What  is  its  ac- 
tion on  animal  organs  placed  in  it?  On  fresh  blood?  On  the  skin 
when  evaporation  is  permitted? 


DILUTED  ALCOHOL.  347 

sensation  of  coolness.  This  is  succeeded  by  a  feeling  of 
warmth  in  the  part;  which  also  becomes  red  from  tempo- 
rary paralysis  of  its  blood-vessels,  causing  them  to  dilate. 
If  the  evaporation  be  prevented,  as  by  putting  a  little  alco- 
hol on  the  skin  and  covering  it  with  a  thimble,  the  alcohol 
acts  as  an  irritant;  it  causes  smarting,  and  finally  sets  up 
inflammation. 

On  mucous  membranes  alcohol  acts  much  as  on  the  skin, 
but  its  irritant  effect  is  more  marked.  Placed  on  the  tongue 
it  causes  a  feeling  of  coolness,  followed  by  a  hot  biting  sen- 
sation, and  a  red  congested  condition  of  the  area  with  which 
it  came  in  contact.  Introduced  into  the  stomach  of  a 
rabbit  or  dog,  where  it  cannot  readily  evaporate,  strong 
alcohol  causes  congestion  and  inflammation  varying  in  in- 
tensity with  its  amount.  If  the  dose  is  large  the  animal 
dies  almost  instantly,  because  the  powerfully  irritated  sen- 
sory nerves  of  the  gastric  mucous  membranes  reflexly  ex- 
cite a  nerve-centre  which  stops  the  heart's  beat. 

Diluted  Alcohol  does  not  produce  the  above-described 
direct  actions  of  the  pure  liquid:  this  latter  taken  into  the 
stomach  acts  as  a  powerful  irritant  poison,  and  generally 
produces  its  main  effects  on  the  stomach  itself.  Alcohol  in 
such  proportion  as  it  exists  in  most  alcoholic  drinks  exerts 
much  less  local  action  on  the  gastric  mucous  membrane;  but 
it  is  absorbed  and  carried  in  the  blood  and  lymph  through 
the  body,  and  if  steadily  taken  day  after  day  acts  upon  and 

When  evaporation  is  prevented?  Action  on  mucous  membranes? 
Illustrate  by  tongue.  By  stomach. 

How  does  strong  alcohol  when  swallowed  sometimes  cause  sud- 
den death? 

How  does  the  action  of  dilute  alcohol  differ  from  that  of  concen- 
trated? What  results  follow  its  frequent  absorption?  What  condi- 
tions influence  the  organs  soonest  injured?  Why  are  alcoholic  dis- 
c-uses often  not  recognized  until  incurable? 


348  THE  HUMAN  BODY. 

alters  for  the  worse  nearly  every  important  organ.  The 
organ  first  or  most  seriously  attacked  varies  with  the  form 
in  which  the  alcohol  is  taken,  with  the  amount  consumed 
daily,  and  with  the  constitution  of  the  individual.  Prob- 
ably no  one  individual  ever  suffered  from  all  the  diseased 
states  produced  by  alcohol  described  in  the  following 
pjiges;  but  habitual  drinkers  are  very  apt  to  experience 
one  or  more  of  them.  The  diseases  produced  by  alco- 
hol after  absorption  into  the  blood  come  on  so  grad- 
ually (except  in  the  case  of  obvious  drunkards)  that  the 
victim  rarely  perceives  them  until  serious  if  not  irreme- 
diable damage  has  been  done:  indeed,  physicians  have  only 
recently  come  to  clearly  recognize  that  men  who  in  com- 
mon phrase  "were  never  in  their  lives  under  the  influence 
of  liquor"  may  nevertheless  be  drinking  enough  to  do 
them  grave  injury. 

Absorption  of  Alcohol.— When  alcohol  (so  diluted  as  not 
to  cause  active  inflammation  of  the  stomach)  is  swallowed, 
it  is  quickly  absorbed  by  the  capillary  blood-vessels  of  the 
gastric  mucous  membrane.*  These  pass  it  on  to  the  portal 
vein,  which  carries  it  (p.  208)  direct  to  the  liver.  Collected 
from  the  liver  by  the  hepatic  veins  it  is  conveyed  through 
the  inferior  vena  cava  to  the  right  auricle  of  the  heart. 
Thence  it  passes  on  in  the  general  blood-flow  (pp.  198, 199, 

Can  a  man  who  drinks  but  is  never  drunk  he  injured  by  alcohol? 

By  what  vessels  is  alcohol  first  absorbed?  To  wliat  vessel  do 
they  carry  it?  Describe  its  further  course  to  the  right  auricle  of  the 
heart.  From  there  to  the  left  auricle. 

*  An  exception  to  the  rapid  absorption  of  alcohol  sometimes  occurs  when  a  large 
quantity  of  raw  spirits  is  taken.  Many  cases  are  recorded  where  men  have  for 
a  wager  drunk  a  bottle  of  whiskey  or  brandy.  The  result  is  often  sudden  death ; 
but  sometimes  no  effect  is  noticed  for  fifteen  or  twenty  minutes ;  then  there  is 
s-adden  unconsciousness,  passing  into  stupor,  which  ends  in  death.  In  such  cases 
tha  large  quantity  of  strong  spirits  seems  temporarily  to  paralyze  the  absorbing 
power  of  the  stomnch. 


PRIMARY  EFFECTS  OF  ALCOHOL.  349 

209)  to  right  ventricle,  lungs,  left  auricle,  left  ventricle, 
aorta,  and  by  branches  of  the  aorta  to  the  body  in  general: 
to  the  heart-muscle  (by  the  coronary  arteries,  p.  202),  to  the 
brain  and  spinal  cord,  to  the  muscles,  to  the  kidneys,  to 
the  skin.  We  have  to  study  its  action  on  all  these  organs. 

The  Primary  Effects  of  a  Moderate  Dose  of  Diluted  Alco- 
hol, as  a  glass  of  whiskey  and  water,  on  one  unaccustomed 
to  it,  are  to  cause  temporary  congestion  of  the  stomach; 
dilatation  of  blood-vessels  of  the  skin,  indicated  by  the 
flushed  face;  a  more  rapid  and  forcible  beat  of  the  heart;* 
nervous  excitement,  exhibited  by  restlessness  and  talkative- 
ness. Then  some  incoherence  of  ideas,  and  often  giddi- 
ness. Finally  there  is  a  tendency  to  sleep.  On  awaking 
the-  person  has  some  feeling  of  depression,  not  much  ap- 
petite, and  is  in  general  a  little  out  of  sorts  for  a  day. 

If  the  dose  be  larger  the  stage  of  giddiness  is  accompanied 
by  diminution  of  the  sensibility  of  the  skin;  and  imperfect 
control  over  the  voluntary  muscles,  indicated  by  defective 
articulation  and  a  staggering  gait.  The  muscles  moving 
the  eyeballs  cease  to  work  in  harmony.  Normally  they 
act  unconsciously,  turning  the  eyes  so  that  images  of 
objects  looked  at  are  focussed  on  corresponding  points 
of  the  retinas;  and  objects  are  seen  single.  Soon  after 
the  voluntary  movements  are  affected  the  involuntary 
regulation  of  the  eye-muscles  is  impaired,  and  objects  are 
seen  double;  the  eyeballs  being  no  longer  so  turned  as  to 
bring  images  on  corresponding  retinal  points.  The  stom- 

Name  important  organs  to  which  the  alcohol  is  ultimately  carried 
in  the  blood. 

Describe  the  primary  effects  of  a  moderate  dose  of  dilute  alcohol. 
Of  a  larger  but  not  fatal  dose. 

*It  is  doubtful  if  chemically  pure  alcohol  diluted  with  water  quickens  the 
pulse;  "lost  ordinary  alcoholic  beverages,  however,  undoubtedly  do. 


350  THE  HUMAN  BODY. 

ach  may  also  be  so  irritated  as  to  lead  to  vomiting.  Then 
comes  deep  drunken  sleep;  followed  by  headache,  loss  of 
appetite,  and  prostration  similar  to,  but  more  marked  than, 
that  occurring  after  the  smaller  dose. 

If  the  alcoholic  indulgence  be  repeated,  day  after  day, 
some  of  the  above-described  primary  consequences  become 
less  marked;  but  they  give  way  to  more  serious  functional 
and  structural  diseases. 

The  Secondary  Effects  of  Alcohol  vary  much  in  inten- 
sity with  the  form  in  which  it  is  taken;  also,  no  doubt, 
flith  the  constitution  of  the  person  taking  it,  and  with 
the  length  of  time  during  which  he  has  been  drink- 
ing. We  shall  consider  them,  in  three  groups:  I.  Compa- 
ratively slight  and  curable  diseased  states  due  to  what 
is  commonly  considered  moderate  drinking.  II.  Severe 
acute  alcoholic  diseases.  III.  Chronic  and  usually  incur- 
able morbid  states,  due  to  steady  prolonged  drinking; 
these  fall  into  three  main  subdivisions:  a.  General  tissue- 
deterioration;  7).  Destruction,  more  or  less  complete,  of  cer- 
tain organs;  c.  Deterioration  of  mind  and  character. 

I.  Minor  Diseased  Conditions  produced  by  Moderate 
Drinking.  —  Of  these,  alcoholic  dyspepsia  is  the  most 
frequent.  A  vast  number  of  persons  suffer  from  it 
without  knowing  its  cause;  people  who  were  never  drunk 
in  their  lives,  and  consider  themselves  very  temperate. 
"  The  symptoms  vary,  but  when  slight  are  something  like 
these:  A  man  (or  woman)  complains  of  slight  loss  of  appe- 
tite, especially  in  the  morning  for  breakfast;  feels  languid 
either  on  rising  or  early  in  the  day;  retches  a  little  in  the 

"What  happens  if  the  dose  of  alcohol  be  taken  day  after  day? 
Classify  the  secondary  actions  of  alcohol  upon  the  body. 
Give  an  account  of  alcoholic  dyspepsia. 


ACUTE  ALCOHOLIC  DISEASES.  351 

morning,  and  perhaps  brings  up  a  little  phlegm  only,  or 
may  actually  vomit;  or  may  be  able  to  take  breakfast 
but  feels  sick  after  it.  Towards  the  middle  of  the 
morning  he  is  heavy  and  languid,  perhaps,  and  does  not 
feel  easy  until  he  has  had  a  glass  of  sherry  or  some  spirits, 
then  gets  on  pretty  well,  and  can  eat  lunch  or  dinner.  Or 
if  worse,  the  appetite  for  both  is  defective,  and  there  is 

undue  weight  or  discomfort  after  meals Now  all 

these  symptoms  may  be  due  to  other  causes,  but  when 
taken  together  they  are  by  far  most  commonly  due  to  al- 
cohol." * 

Another  frequent  result  of  regular  "moderate"  drinking 
is  tremor,  orshakiness  of  the  hands.  The  hand  is  unsteady 
when  the  arm  is  folded,  and  is  seen  to  tremble  if  it  be  held 
out  with  the  arm  extended.  This  tremor  is  very  marked 
in  the  alcoholic  disease  known  as  delirium  tremens  (p.  352). 
Even  in  its  simple  form  it  interferes  with  the  performance 
of  any  action  calling  for  manual  dexterity.  The  trembling 
may,  in  most  cases,  be  stopped  for  a  time  by  an  extra  glass; 
and  thus  often  leads  to  the  acquirement  of  more  serious 
diseases. 

We  class  the  above  as  minor  diseased  conditions,  because 
in  most  cases  they  occur  before  the  will-power  is  seriously 
impaired,  and  abstinence  from  alcohol  is  soon  followed  by 
recovery. 

II.  Acute  Alcoholic  Diseases. — A  single  large  dose  of  alco- 

Describe  alcoholic  tremor.  In  what  disease  is  it  very  marked  ? 
What  results  from  even  its  simple  form?  How  does  it  often  lead  to 
the  acquirement  of  more  serious  alcoholic  disease? 

Why  do  we  class  the  dyspepsia  and  tremor  as  minor  alcoholic  dis- 
eases ? 

What  results  from  a  large  dose  or  repeated  small  doses  of  alcohol  ? 

*  Dr.  Greenfield,  in  "  Alcohol:  its  Use  and  Abuse." 


353  THE  HUMAN  BODY. 

hoi,  or  the  repetition  of  small  doses  at  shert  intervals,  ends 
in  a  fit  of  drunkenness. 

The  disgusting  appearance  of  a  drunken  man,  the  loath- 
ing which  he  excites  even  in  those  most  attached  to  him, 
the  loss  of  control  over  his  actions,  which  makes  him  the 
prey  of  criminals,  or,  yet  worse,  a  criminal  himself,  taken 
together  make  a  picture  to  which  the  physiologist  need  add 
nothing.  A  man  not  deterred  by  its  contemplation  will 
not  be  hindered  in  the  indulgence  of  his  appetite  by  any 
argument  based  on  injury  to  his  health. 

Delirium  Tremens. — Repeated  drunkenness  usually  ends 
in  an  attack  of  delirium  tremens,  but  this  disease  is  more 
frequently  the  result  of  prolonged  drinking  which  has 
never  culminated  in  actual  drunkenness.  It  is  especially 
apt  to  occur  in  "those  who  drink  hard,  but  keep  from 
actual  loss  of  consciousness,  especially  those  engaged  in 
hard  .mental  work  or  subjected  to  great  moral  strain  or 
shock ;  and,  too,  those  of  certain  temperaments  are  pecu- 
liarly liable  to  it.  It  is  preceded,  usually,  by  loss  of  sleep, 
ideas  of  persecution  or  injury,  with  no  foundation  in  fact, 
and  slight  hallucinations,  especially  at  night ;  the  man, 
meanwhile,  in  the  day  looking  anxious,  slightly  excited, 
nervous  and  tremulous,  and  perhaps  narrating  as  actual 
occurrences  the  hallucinations  of  the  preceding  night. 
Then  the  senses  are  partly  lost;  he  sees  spectres,  horrible 
and  foul  creatures  about  him;  has  all  sorts  of  painful,  terri- 
fying visions  (whence  the  common  name  of  the  ' horrors'); 
is  extremely  tremulous,  and  either  excited  or  lies  prostrate, 
trembling  violently  on  movement,  sleepless,  anxious,  and  a 
prey  to  spectres  and  terrors  of  the  imagination."  * 

Under  what  conditions  may  delirium  tremens  occur? 
What  symptoms  usually  precede  this   disease?    Describe  the  con- 
dition of  a  person  suffering  from  delirium  tremens. 

*  Dr.  Greenfield,  in  "  Alcohol:  its  Use  and  Abuse.'" 


DELIRIUM  TREMENS.  353 

Few  persons  di^in  their  first  attack  of  delirium  tremens, 
but  it  is  nature's  unmistakable  warning  to  the  tippler;  let 
him  not  disregard  it,  unless  he  is  prepared  to  die  without 
hope  in  maniacal  imaginings  so.  frightful  that  those  around 
his  death-bed  can  never  recall  the  scene  without  horror  ! 

Dipsomania  is  often  confounded  with  delirium  tremens, 
but  though  it  may  lead  to  that  disease  it  is  an  essentially 
different  pathological  state.  The  word  properly  means  a 
mental  disease  in  which  there  is  periodically  an  irresistible 
passion  for  alcohol;  in  any  form,  no  matter  how  distasteful, 
the  dipsomaniac  will  swallow  it  with  avidity.  The  disease 
is  sometimes  produced  by  indulgence  in  drink,  but  is  more 
often  inherited,  especially  from  parents  addicted  to  alco- 
holic excess.  In  the  families  of  such,  one  child  is  often 
epileptic,  another  idiotic,  a  third  eccentric  or  perhaps  quite 
mad,  and  a  fourth  a  dipsomaniac.  When  the  fit  seizes  him 
the  dipsomaniac  is  as  irresponsible  as  a  raving  madman. 
His  only  safeguard  against  a  frightful  debauch  is  to  place 
himself  under  restraint  as  soon  as  he  perceives  the  symp- 
toms which  he  has  learned  to  recognize  as  premonitory  of 
his  fit  of  madness.  After  a  time  the  paroxysm  passes  off; 
the  patient  regains  self-control,  loses  his  passion  for  drink, 
is  greatly  ashamed  of  himself  if  he  has  indulged  it,  and 
usually  behaves  in  an  irreproachable  manner  for  some  weeks 
or  months. 

The  sufferers  from  this  frightful  disease  are  entitled  to  a 
sympathy  to  which  the  common  drunkard  has  no  claim. 

III.  Chronic  and  often  Incurable  Diseased  Conditions 
produced  by  Alcohol. — These  are  apt  to  be  insidious  in  their 

What  is  the  proper  meaning  of  the  word  dipsomania?  What  dis- 
eases are  apt  to  be  found  in  the  children  of  parents  given  to  alcoholic 
excess?  What  should  a  dipsomaniac  do  Avhen  he  feels  the  fit  coming 
or  ?  What  happens  when  the  paroxysm  passes  off? 


354  THE  HUMAN  BODY. 

approach,  and  overlooked  until  they- have  firmly  seated 
themselves.  They  include,  (a)  deterioration  of  tissue;  (b) 
practical  destruction  of  important  organs;  (c)  mental  and 
moral  enfeeblement. 

(a)  Deterioration  of  Tissue  due  to  Alcohol. — A  serious 
structural  change  in  the  body  produced  by  alcoholic  excess 
is  fatty  degeneration.  The  oily  matter  of  the  body  exists 
in  two  forms:  first,  as  adipose  or  fatty  tissue  collected 
under  the  skin,  and  in  less  amount  elsewhere,  as  on  the 
surface  of  the  heart  and  around  the  kidneys;  second,  as 
minute  fat-droplets  in  the  interior  of  various  cells  and  fibres. 
Some  forms  of  alcoholic  drinks  tend  to  increase  the 
adipose  tissue,  and  may  lead  to  undue  accumulation  of  it 
about  the  heart,  impeding  the  action  of  that  organ.  A 
more  important  and  frequent  result  is  an  increase  of  fat- 
droplets  in  the  cells  of  the  liver  and  the  muscular  fibres  of 
the  heart,  the  oily  matter  replacing  the  natural  working 
substance.  A  heart  which  has  undergone  this  change  is 
commonly  spoken  of  by  pathologists  as  a  "whiskey  heart;" 
for  although  fatty  degeneration  of  the  heart  may  occur 
from  other  causes,  alcoholic  indulgence  is  the  most  frequent 
one.  Fatty  liver  or  fatty  heart  is  rarely  if  ever  curable; 
either  will  ultimately  cause  death.  It  is  probable  that  in 
both  cases  the  fatty  degeneration  is  due  to  over-stimulation 
of  the  organ.  Most  wines  and  spirits  quicken  the  beat  of 
the  heart,  leaving  it  less  time  for  repair  between  its  strokes. 


"Why  are  chronic  alcoholic  diseases  often  unnoticed  in  their  curable 
stages?  What  main  forms  do  they  include? 

In  what  forms  is  the  oily  matter  of  the  body  found?  How  do  some 
forms  of  alcohol  affect  the  development  of  adipose  tissue?  What 
may  result?  How  does  alcohol  produce  more  serious  changes  in  the 
fatty  matter  of  the  body?  What  is  meant  by  a  "  whiskey  heart"? 

What  is  the  consequence  of  fatty  liver  or  fatty  heart?  To  what 
is  the'fatty  degeneration  in  these  organs  due?  Explain  i'or  the  heart. 


ALCOHOLIC  DETERIORATION  OF  TISSUE.        355 

Alcohol  also  increases  the  breaking  down  of  proteid  matter 
in  the  body;  the  liver  has  much  to  do  in  preparing  this 
broken-down  proteid  for  removal  by  the  kidneys,  and  so 
gets  overworked. 

Another  serious  bodily  deterioration  produced  by  alco- 
hol is  fibrous  degeneration :  by  this  is  meant  an  excessive 
growth  of  the  connective-tissue,  which  as  we  have  seen 
(p.  24)  pervades  the  organs  of  the  body  as  a  fine  sup- 
porting skeleton  for  the  more  essential  cells.  Alcohol- 
drinking  causes  this  tissue  to  develop  to  such  an  extent  as 
to  crush  and  destroy  the  cells,  especially  in  the  liver  and 
kidneys,  which  it  should  protect.  So  far  as  the  liver  is  con- 
cerned, the  result  is  a  shrunken,  rough  mass  (hob-nailed 
liver 9  or  gin-drinker's  liver),  with  hardly  any  liver-cells  left 
in  ifc.  This  not  only  prevents  the  proper  manufacture  of 
bile  and  glycogen  (p.  151),  but  the  contracted  liver  presses 
on  the  branches  of  the  portal  vein  within  it  (p.  208)  so  as  to 
impede  the  drainage  of  blood  from  the  organs  in  the  abdo- 
men. As  a  consequence,  an  excess  of  the  watery  part  of 
the  blood  oozes  into  the  peritoneal  cavity  and  accumulates, 
causing  abdominal  dropsy  (ascites).  In  similar  manner  the 
superabundant  connective  tissue  in  the  kidneys  crushes 
and  injures  the  essential  kidney  substance,  and  interferes 
with  the  proper  function  of  the  organ  in  excreting  nitrogen 
waste  and  water.  The  ultimate  consequence  is  one  form  of 
"  Bright's  disease" — a  very  fatal  malady,  characterized  by 
elimination  of  albumen  in  the  kidney  secretion;  retention 
of  proteid  wastes  in  the  blood,  poisoning  the  various 
organs;  and  accumulation  of  water  in  the  loose  tissue  bind- 

Explain  for  the  liver. 

What  is  fibrous  degeneration?  Describe  the  results  wh?n  it  occurs 
in  the  iiver.  In  the  kidneys. 

What  are  the  characteristics  of  Bright's  disease? 


356  THE  HUMAN  BODY. 

ing  the  skin  to  underlying  parts,  producing  that  kind  ot 
dropsy  known  as  anasarca. 

(b)  The  Organs  of  the  Body  most  apt  to  be  impaired  or 
destroyed  by  Alcohol  have  been  in  part  mentioned  in  pre- 
ceding pages.  It  will,  however,  be  convenient  to  collect 
them  together,  and  point  out  the  kind  of  change  produced 
in  each.  Probably  no  tippler  ever  suffered  from  all  of 
these  diseases,  and  most  of  them  may  develop  in  persons 
who  are  total  abstainers;  but  the  organic  lesions  which  are 
mentioned  below  are  more  frequently  due  to  intemperance 
than  to  any  other  cause. 

A  primary  action  of  alcohol  after  absorption  is  to  cause 
dilatation  of  the  cutaneous  blood-vessels.  'With  occasional 
alcoholic  indulgence  this  is  temporary;  with  repeated,  it  be- 
comes permanent.  The  Skin  is  then  congested  and  puffy, 
and  on  exposed  parts  it  is  seen  to  have  a  purplish  or  red- 
dish blotched  appearance;  pimples  appear  on  parts,  such 
as  the  nose,  where  the  natural  circulation  is  more  feeble. 
The  result  is  the  peculiar  degraded  look  of  the  sot's  face. 
The  congestion  interferes  with  the  nutrition  of  the  skin; 
the  epidermis  (p.  266)  is  imperfectly  nourished  and  collects 
in  scaly  masses,  interfering  with  the  proper  action  of  the 
sweat-glands,  thus  throwing  undue  work  on  the  kidneys. 

When  constantly  irritated  by  the  direct  action  of  strong 
alcoholic  drinks,  the  Stomach  gradually  undergoes  lasting 
changes.  Its  vessels  remain  dilated  and  congested,  its 
connective  tissue  becomes  excessive,  its  power  of  secreting 
gastric  juice  diminished,  and  its  mucous  secretion  abnor- 
mally abundant. 

The  Liver  suffers  fatty  and  fibrous  degeneration,  and  is 

Describe  the  consequences  of  alcoholic  indulgence  on  the  skin 
On  the  stomach. 


ORGANS  INJURED  BY  ALCOHOL.  357 

one  of  the  organs  most  often  and  earliest  attacked.  This 
we  might  expect,  as  all  the  alcohol  absorbed  from  the  stom- 
ach is  carried  direct  to  the  liver  by  the  portal  vein  (p.  208). 

The  Heart  has  its  walls  at  first  thickened  (Jiypertrophied) 
and  its  cavities  dilated  by  the  excessive  work  (p.  354)  which 
alcoholic  drinks  stimulate  it  to  perform.  If,  as  is  usually 
the  case,  fatty  degeneration  ensues,  the  organ  gradually 
becomes  too  feeble  to  pump  the  blood  around  the  body, 
and  death  results. 

The  walls  of  the  Arteries  of  drinkers  frequently  undergo 
fatty  degeneration;  they  lose  their  strength  and  elasticity, 
and  are  liable  to  rupture,  or  to  the  disease  known  as  aneu- 
rism. 

The  Kidneys  are  excited  to  undue  activity,  in  part  by 
the  dilatation  of  their  blood-vessels,  in  part,  perhaps, 
through  direct  stimulation  of  their  cells  by  alcohol  circu- 
lating in  the  blood.  Once  the  liver  is  attacked  the  nitro- 
genous waste  of-  the  body  is  not  carried  to  the  kidneys  in 
proper  form  for  excretion:  some  is  held  back,  producing  a 
tendency  to  gout  and  rheumatism  ;  the  rest  is  got  rid  of  by 
extra  kidney  effort.  The  usual  result  is  fibrous  degenera- 
tion of  the  kidneys,  causing  one  kind  of  Blight's  disease. 

The  Lungs,  from  the  congested  state  of  their  vessels  pro- 
duced uy  alcohol,  are  more  subject  to  the  influence  of  cold, 
the  result  being  frequent  attacks  of  bronchitis.  It  has  also 
been  recognized  of  late  years  that  there  is  a  peculiar  form 
of  consumption  of  the  lungs  which  is  very  rapidly  fatal,  and 
found  only  in  alcohol-drinkers. 

On  the  liver?  Why  is  the  liver  especially  apt  to  be  attacked?  On 
the  heart?  On  the  arteries? 

How  does  alcohol  affect  the  kidneys  directly?  How  through  the 
liver-disease  produced  by  it?  What  results? 

What  lung-diseases  are  often  produced  by  alcohol? 


358  THE  HUMAN  BODY. 

The  Sense-organs  are  also  affected:  their  acuteness  of  per- 
ception is  dulled;  and  many  physicians  believe  that  cata- 
ract and  retinal  disease  may  be  produced  by  drinking.  The 
red  inflamed  white  of  the  eye  of  topers  is  well  known. 

The  Brain  and  Spinal  Cord  are  kept  in  a  chronic  state  of 
congestion*  and  over-excitement.  This  results  at  first  in  in- 
flammatory disease  (delirium  tremens);  later,  in  fibrous  de- 
generation, leading  to  certain  forms  of  paralysis  or  to  epi- 
lepsy, of  which  there  is  one  variety  well  recognized  by  phy- 
sicians as  due  to  alcohol. 

(c)  Moral  Deterioration  produced  by  Alcohol. — One  re- 
sult of  a  single  dose  of  alcohol  is  that  the  control  of  the 
Will  over  the  actions  and  emotions  is  temporarily  enfeebled; 
the  slightly  tipsy  man  laughs  and  talks  loudly,  says  and 
does  rash  things,  is  enraged  or  delighted  without  due  cause. 
If  the  amount  of  alcohol  be  increased,  further  diminution 
of  will-power  is  indicated  by  loss  of  control  over  the  mus- 
cles. Excessive  habitual  use  of  alcohol  results  in  perma- 
nent over-excitement  of  the  emotional  nature  and  en- 
feeblement  of  the  Will;  the  man's  highly  emotional  state 
exposes  him  to  special  temptation  to  excesses  of  all 
kinds,  and  his  weakened  Will  decreases  the  power  of 
resistance:  the  final  outcome  is  a  degraded  moral  condi- 
tion. He  who  was  prompt  in  the  performance  of  duty  be- 

Describe  the  action  of  alcohol  on  the  sense-organs.   On  the  brain  and 
spinal  cord,  and  the  resulting  diseases. 
Describe  the  moral  deterioration  produced  by  alcohol. 

*  "  I  once  had  the  unusual  though  unhappy  opportunity  of  observing  the  same 
phenomenon  in  the  brain-structure  of  a  man  who,  in  a  fit  of  alcoholic  excitement, 
decapitated  himself  under  the  wheel  of  a  railway-carriage,  and  whose  brain  was 
instantaneously  evolved  from  the  skull  by  the  crash.  The  brain  itself,  entire,  was 
before  me  within  three  minutes  after  death.  It  exhaled  the  odor  of  spirit  most 
distinctly,  and  its  membranes  and  minute  structures  were  vascular  in  the  ex- 
treme. It  looked  as  if  it  had  been  recently  injected  with  vermillion."— Dr.  B.  W. 
Richardson. 


TEE  OPIUM  HABIT.  359 

gins  to  shirk  that  which  is  irksome;  energy  gives  place  to 
indifference,  truthfulness  to  lying,  integrity  to  dishonesty; 
for  even  with  the  best  intentions  in  making  promises  or 
pledges  there  is  no  strength  of  Will  to  keep  them.  In  for- 
feiting the  respect  of  others  respect  for  self  is  lost  and 
character  is  overthrown.  Meanwhile  the  passion  for  drink 
grows  absorbing:  no  sacrifice  is  too  costly  which  secures  it. 
Swift  and  swifter  is  now  the  downward  progress.  A  mere 
sot,  the  man  becomes  regardless  of  every  duty,  and  even  in- 
capacitated for  any  which  momentary  shame  may  make 
him  desire  to  perform. 

For  such  a  one  there  is  but  one  hope — confinement  in 
an  asylum  where,  if  not  too  lute,  the  diseased  craving  for 
drink  may  be  gradually  overcome,  the  prostrated  Will  re- 
gain its  ascendency,  and  the  man  at  last  gain  the  victory 
over  the  'brute. 

Opium  and  Morphia. — Opium  is  a  gummy  mixture  con- 
taining several  active  principles,  of  which  the  most  impor- 
tant is  morphia.  The  forms  in  which  it  is  most  frequently 
employed  are  (1)  gum  opium,  the  crude  substance,  often 
put  up  in  the  form  of  pills;  (2)  laudanum,  an  alcoholic 
extract  of  the  gum;  (3)  paregoric,  a  liquid  containing  sev- 
eral substances,  of  which  opium  is  the  most  important; 
(4)  morphia  and  its  compounds. 

The  Opium  Habit. — Opium  is  perhaps  the  most  valuable 
drug  at  the  disposal  of  the  physician.  On  the  other  hand, 
it  is  one  of  the  most  injurious  substances  used  by  mankind. 
It  may  be  that  it  does  not  do  so  much  harm  in  the  United 
States  as  alcoholic  drinks,  but  only  because  not  so  many 

What  is  the  confirmed  drunkard's  only  hope  for  cure? 
What  is  opium  ?    In  what  forms  is  it  most  often  used? 
Compare  the  damage  done  in  the  United  States  by  indulgence  in 
alcohol  and  opium. 


360  THE  HUMAN  BOD7. 

persons  have  acquired  the  craving  for  it.  Used  constantly 
it  is  as  certainly  fatal  and  the  habit  is  perhaps  even  harder  to 
break;  for  it  may  be  indulged  more  secretly  and  its  effects 
are  not  so  readily  recognized.  There  is  also  this  to  be 
said:  that  most  inebriates  are  originally  of  weak  character, 
wrecking  themselves  on  a  rock  in  full  view,  through  lack  of 
a  strong  hand  at  the  helm;  while  many  a  one  of  highest 
gifts  and  noblest  character,  who  would  loathe  the  low  vice 
of  drunkenness,  has  gone  under  in  the  insidious  maelstrom 
spread  by  opium  for  its  victims.  Using  the  drug  at  first 
as  prescribed  for  the  relief  of  suffering,  he  (or  she,  for  more 
women  than  men  are  addicted  to  opium  excess)  is  scarcely 
conscious  of  danger  before  being  swept  on  to  destruction. 
Most  medical  men  now  fully  recognize  the  danger  and  only 
order  prolonged  use  of  opium  with  great  caution.  Never- 
theless tli ere  are  so  many  persons  who  habitually  use  opium 
that  it  is  important  to  point  out  the  disastrous  results. 

The  Diseased  Conditions  produced  by  Regular  Use  of  Opium 
are  fairly  uniform.  The  first  phenomenon  is  deadening  of 
sensibility,  accompanied  by  mental  exaltation  if  the  dose  be 
small.  This  is  succeeded  by  unnatural  sleep,  disturbed  by 
fantastic  dreams. 

On  awaking  there  is  great  depression  of  mind  and  body: 
often  associated  with  defective  memory,  and  a  feeling  that 
something  terrible  is  about  to  happen.  There  is  muscular 
weakness;  distaste  for  food,  without  actual  nausea;  and  an 
almost  irresistible  craving  for  another  dose. 

If  the  habit  be  continued  further,  mental  and  physical 
changes  occur.  Distaste  and  inaptitude  for  any  kind  of 

Why  is  opium  more  disastrous  from  one  point  of  view? 
What  are  the  first  phenomena  following  a  dose  of  opium?    What 
is  the  condition  of  the  person  on  awaking? 
What  results  follow  continuance  of  the  habit? 


CHLORAL.  361 

exertion;  greatly  impaired  digestion;  deficient  secretion  of 
bile;  sluggishness  of  the  muscles  of  the  intestines,  causing 
constipation.  The  muscles  waste,  the  skin  shrivels,  and 
the  person  looks  prematurely  aged.  The  pulse  is  quick, 
the  body  feverish;  the  eye  dull,  except  just  after  the  drug 
has  been  taken. 

The  final  result  is  failure  of  the  nervous  system.  Incom- 
plete paralysis  of  the  lower  limbs  is  followed  by  a  similar 
state  of  the  muscles  of  the  back.  The  victim  crawls  along, 
bent  like  an  old  man.  Death  finally  results  from  starva- 
tion, due  to  complete  failure  of  the  digestive  org.-ms. 

Morphia. — When  morphia  is  used,  a  solution  of  it  is  often 
injected  under  the  skin  by  a  fine  syringe.  Prolonged  use 
of  it  in  this  way  is  followed  by  all  the  symptoms  of  chronic 
opium-poisoning  above  described.  The  digestive  organs 
are  not,  however,  as  soon  attacked;  but  the  punctures  of 
the  skin  repeated  for  weeks,  several  times  a  day,  cause  in- 
flammation and  ulcemtion. 

Danger  of  administering  Opiates  to  Children. — Children 
are  remarkably  sensitive  to  opium  and  all  preparations  con- 
taining it.  Opiates  should  never  be  administered  to  children 
except  by  order  of  a  physician.  Many  an  infant  has  been 
poisoned  by  a  few  drops  of  paregoric  or  of  some  soothing 
syrup  given  by  parent  or  nurse  to  check  diarrhoea  or  pro- 
duce sleep. 

Chloral, — The  chloral  habit  is  in  this  country  at  present 

What  is  the  final  result? 

In  what  do  the  consequences  of  injection  of  morphia  beneath  the 
skin  resemble  and  differ  from  those  of  opiates  taken  by  the  mouth? 

How  are  children  peculiar  as  regards  opiates?  Under  what  condi- 
tions only  should  they  be  administered  to  children?  What  often  re- 
sults from  giving  opiates  to  infants? 

Compare  the  frequency  of  the  chloral  and  opium  habits  in  the 
United  States. 


362  THE  HUMAN  BODY. 

more  common  than  the  opium  habit,  and,  like  it,  more  fre- 
^aent  among  women  than  men. 

Chloral  was,  on  its  discovery  a  few  years  ago,  heralded 
as  a  wonderfully  safe  and  certain  promoter  of  sleep,  and  al- 
leviator of  pain.  Medical  men  have  since  learned  that  it  is 
by  no  means  so  harmless  a  drug  as  they  once  believed;  but 
the  general  public  do  not  seem  to  have  had  their  eyes 
opened  to  its  danger.  A  great  many  preparations  of  it 
have  been  put  on  the  market,  and  aru  sold  in  drug-stores 
to  all  comers.  The  result  is  that  many  persons  who  would 
hesitate  to  take  opium  without  medical  advice  use  chloral, 
believing  it  harmless. 

Chloral,  taken  habitually,  is  at  least  as  mischievous  as 
opium.  It  should  be  forbidden  by  law  to  retail  it  in  any 
form  except  on  the  prescription  of  a  physician. 

The  chloral  habit  is  acquired  with  great  ease,  and  is  very 
hard  to  break.  The  first  phenomena  of  chloral  disease 
(chloralism)  are  these:  The  digestion  is  greatly  impaired; 
the  tongue  is  dry  and  furred;  there  is  nausea;  sometimes 
vomiting,  and  a  constant  feeling  of  oppression  from  wind 
on  the  stomach. 

Next,  nervous  and  circulatory  disturbances  occur.  The 
temper  becomes  irritable,  the  Will  weak;  the  hands  and  legs 
tremulous;  the  heart-beat  irregular;  the  face  easily  flushed. 
Sleep  becomes  impossible  without  use  of  the  drug:  when 
obtained  it  is  troubled,  and  the  person  awakes  unrested. 

In  later  stages  the  blood  is  seriously  altered.  Its  color- 
ing matter  is  dissolved,  and  soaks  through  the  walls  of  the 

What  have  medical  men  lately  learned  about  chloral?  Why 
do  so  many  people  take  chloral  without  medical  advice? 

Describe  the  first  symptoms  of  chlonilism. 

What  are  the  symptoms  in  more  advanced  chloralism?  What  in 
the  latest  stages? 


THE  LOCAL  ACTION  OF  TOBACCO.  363 

capillary  vessels,  causing  purplish  patches   on  the  skin. 
Jaundice  also  frequently  occurs. 

If  the  chloral-biking  be  still  continued,  death  results 
from  impoverished  blood,  weakened  hearc,  or  paralysis  of 
the  nervous  system.  Not  unfrequently  chloral-takers  un- 
intentionally commit  suicide  by  indulging  in  too  large  a 
dose. 

Tobacco  contains  an  active  principle,  nicotin,  which 
in  its  pure  form  is  a  powerful  poison,  paralyzing  the 
heart.  When  tobacco  is  smoked  some  of  the  nicotin  is 
burned,  but  there  are  developed  certain  acrid  vapors  which 
have  an  irritant  action  on  the  mouth  and  throat.  The 
effects  of  smoking  are  thus  in  part  general,  due  to  absorbed 
nicotin;  and  in  part  local,  due  to  irritant  matters  in  the 
smoke.  They  vary  much  with  the  constitution,  habits, 
and  age  of  the  smoker.  One  general  rule  at  least  may  be 
laid  down:  tobacco  is  very  injurious  to  young  persons  whose 
physical  development  is  not  completed. 

The  Local  Action  of  Tobacco  is  at  first  manifested  by  in- 
creased flow  of  saliva.  This  usually  passes  off  after  some 
practice  in  smoking;  dry  ness  of  the  mouth  follows,  and  con- 
sequent thirst,  often  leading  to  alcoholic  indulgence;  and 
in  this,  perhaps,  lies  the  greatest  danger  from  tobacco. 
The  habitual  smoker  usually  suffers  eventually  from  what 
is  known  to  medical  men  as  "  smoker's  sore-throat."  The 
inflammation  often  extends  to  the  larynx,  injuring  the 
voice  and  producing  a  hacking  cough,  or  may  spread  up 

How  does  death  from  chloral  occur? 

What  is  nicotin?  What  other  injurious  substances  are  found  in 
tobacco-smoke?  What  general  rule  may  be  stated  concerning  the 
action  of  tobacco  on  the  human  body? 

Describe  the  local  actions  of  tobacco.  How  may  tobacco-smoking 
injure  the  voice?  How  the  hearing? 


364  THE  HUMAN  BODY. 

the  Eustachian  tubes  (p.  330)  and  impair  the  hearing. 
Cigarettes  are  especially  apt  to  cause  these  symptoms. 
Cure  is  impossible  unless  smoking  be  given  up,  Those 
who  draw  the  smoke  into  their  lungs  often  suffer  from 
chronic  inflammation  of  the  bronchial  tubes  inconsequence. 
The  General  Action  of  Tobacco. — The  more  common 
effects  of  absorption  of  tobacco  products  are  to  interfere  with 
development  of  the  red  blood-corpuscles,  leading  to  pallor 
and  feebleness;  to  impair  the  appetite  and  weaken  digestion; 
to  affect  the  eyes,  rendering  the  retina  less  sensitive;  to 
cause  palpitation  of  the  heart  and  enfeeblement  of  that 
organ;  to  induce  a  lassitude  and  indisposition  to  exer- 
tion that,  in  view  of  the  heavy  odds  man  has  to  contend 
with  in  the  life-struggle,  may  prove  the  handicap  that 
causes  his  failure.  If  success  in  life  be  an  aim  worth  striv- 
ing for,  it  is  surely  unwise  to  shackle  one's  self  with  a  habit 
which  cannot  promote  and  may  seriously  jeopardize  it. 

Describe  the  general  action  of  tobacco  on  the  body. 


INDEX. 


ABDOMINAL  aorta,  202 

Abdominal  cavity,  11 

Abdominal  respiration,  246 

Abducentes  nerves,  292 

Abduction,  63 

Absorbents,  107.  188;  relation  of 
to  excretion,  108 

Absorption,  from  the  month, 
pharynx  and  gullet,  166;  from 
the  stomach,  167;  from  the 
small  intestine,  167;  from  the 
large  intestine,  168;  of  fats, 
162 

Accommodation,  326 

Acetabulum,  60 

Acid,  glycocholic,  161;  hydro- 
chloric, 20,  157;  oleic,  21;  pal- 
mitic, 21;  stearic,  21;  tauro- 
cholic,  161 

Acinous  glands,  129,  131 

Adam's  apple,  338 

Adduction,  63 

Afferent  (sensory)  nerves,  305 

Air,  changes  produced  in  by 
being  breathed,  251;  necessary 
quantity  of  for  each  person, 
255 ;  quantity  of  breathed  daily, 
250 j  renewal  of  in  the  lungs, 
240;  unwholesome,  254 

Air-cells,  237 

Air-passages,  234;  cilia  of,  236 

Albumen,  egg,  21,  117;  serum, 
21,  113 

Albuminoid  alimentary  prin- 
ciples, 117 

J  Albuminous  (proteid)  substances, 
21;  action  of  bile  on,  161;  of 
gastric  juice  on..  157;  of  pan- 
creatic secretion  on,  159,  172; 
special  importance  of  as  food, 
111 

Alcoliol,  121,  343;  absorption  of, 
348;  diseases  produced  by,  350 > 
is  it  a  food,  121,  343;  mental 


Alcohol  (Continued). 
and  moral  deterioration  due  to, 
353,  358 

Alimentary  canal,  9,  106;  absorp- 
tion from,  166;  anatomy  of, 
169;  general  arrangement  of, 
128;  sub-divisions  of,  132 

Alimentary  principles,  116;  al- 
buminoid, 117;  carbohydrate, 
118;  hydrocarbon,  117";  inor- 
ganic, 118;  proteid,  117 

Amoeba,  179 

Amyloids  (see  Carbohydrates) 

Anaemia,  185 

Anatomy,  human,  2,  17 

Anatomy,  microscopic  (see  His. 
tology) 

Anatomy,  of  alimentary  canal, 
132,  169;  of  circulatory  organs, 
192;  of  ear,  329;  of  eyeball, 
321;  of  joints,  60;  of  larynx, 
337;  of  liver,  149:  of  muscular 
system,  67;  of  nervous  system, 
282,  299;  of  respiratory  organs, 
233;  of  skeleton,  23;  of  skin, 
266;  of  uriuaiy  organs,  261, 
278 

Animals,  classification  of,  8  (foot- 
note) 

Animal  charcoal,  55 

Animal  heat,  96 

Ankle  joint,  83 

Aorta,  198,  212;  thoracic,  202; 
abdominal,  202 

Apex  beat  (cardiac  impulse),  217 

Apex  of  heart,  195 

Appendicular  skeleton,  26 

Appetite,  cause  of,  165 

Aqueous  humor,  325 

Arachnoid,  286 

Arch  of  foot,  42.  45 

Areolar  tissue,  subcutaneous,  268 

Arm,  skeleton  of,  28 

Arterial  blood,  178,  211 


366 


INDEX. 


Arterial  pressure,  227 

Arteries,  195,  202;  action  of 
alcohol  on,  357;  aorta,  198, 
212;  axillary,  202;  brachial, 
202;  coeliac  axis,  202;  com- 
mon iliacs,  204;  coronary. 
199,  202,  213;  femoral,  204, 
hepatic,  150;  left  common 
carotid,  202;  left  subcluvian, 
202;  mesenteric,  202;  peroueal, 
204;  popliteal, 204;  pulmonary, 
199,  212;  radial,  202,  222; 
renal,  202,  261;  right  common 
carotid,  202;  right  subclavian, 
202;  temporal,  222;  tibial,  204; 
ulimr,  202 

Arteries,  course  of  the  main,  201; 
muscles  of  the,  228:  properties 
of  the,  204;  why  placed  deep, 
205 

Articular  cartilage726,  48 

Articular  extremities  of  bones,  48 

Articulations,  25 

Arytenoid  cartilages,  338 

Assimilation,  108 

Astragalus,  40 

Atlanto-axial  articulation,  32 

Atlas  vertebra,  32 

Auditory  nerve,  293 

Auditory  organ,  329 

Auricles,  197;  function  of  the,220 

Auricular  appendages,  213 

Auricular  contraction,  217 

Auriculo-ventiicular  orifice,  197 

Auriculo- ventricular  valves,  201, 
217;  demonstration  of  their 
action,  232 

Auscultation,  245 

Automatic  nerve  centres,  307; 
use  of,  309 

Axial  skeleton,  26 

Axillary  artery,  202 

Axis  cylinder  of  nerves,  296 

Axis  vertebra,  32 

BACKBONE  (see  Vertebral  column) 
Ball  and  socket  joint(enarthrosis), 

62 

Basement  membrane,  131 
Base  of  heart,  195 
Bathing,  230,  275;   proper  time 

for,  276 


Beans,  nutritive  value  of,  121 

Beef -tea,  77 

Beeswax,  118 

Beverages,  alcoholic,  346 

Biceps  muscles,  definition  of,  71 

Biceps  muscle,  69,  72 

Bicuspids  (premolars),  136 

Bile,  150,  161;  action  of  in  fat 
absorption,  162,  172;  uses  of, 
161 

Bile  duct,  common  (duct us  com- 
munis  choledochus),  150,  170 

Bi-penniform  muscles,  71 

Bladder,  urinary,  263,  278 

Blind  spot,  324 

Blood,  action  of  oxygen  on,  de- 
monstration, 259;  arterial  and 
venous,  178,  211;  changes  un- 
dergone by  in  the  lungs,  257; 
circulation  of,  207;  coagulation 
of,  179;  colorless  corpuscles  of, 
179;  compared  with  water, 
182;  experiments  with,  190; 
flow  of  in  the  capillaries  and 
veins,  224;  functions  of,  174, 
175;  gases  of,  183;  histology 
of,  176  ;  hygiene  of,  184; 
quantity  of  in  the  body,  185; 
red  corpuscles  of,  177 ;  whipped 
(defibrinated),  181 

Blood-plasma,  176 
, Blood  serum,  180,  191;  composi- 
tion of,  182 

Blushing,  228  ' 

Body,  centre  of  gravity  of,  85; 
chemical  composition  of,  19; 
constructive  power  of,  112; 
co-operation  of  the  organs  of, 
279;  daily  need  of  foods  by, 
124;  general  plan  of,  6;  levers 
in  the,  80;  movements  of,  59; 
oxidations  in,  99;  oxygen  food 
of,  103;  pulleys  in,  84;  quan- 
tity of  blood  in,  185;  tempera- 
ture of,  97;  wastes  of,  105 

Bones,  chemical  composition  of, 
54;  fractures  of,  57;  function 
of,  23;  gross  structure  of,  47; 
histology  of,  51 ;  internal  struc- 
ture of,  49 ;  of  cranium,  37 ;  of 
ear,  331,  of  face,  37;  of  lower 
limb,  28;  of  pectoral  arch,  27; 


INDEX. 


367 


Bones  (Continued). 

of  pelvic  arch,  28;  of  upper 
limb,  28:  reason  that  they  are 
hollow,  50;  varieties  of,  51 

Bone-ash,  55 

Bone-black  (animal  charcoal),  55 

Bone  corpuscles,  54 

Bony  skeleton,  26;  hygiene  of,  56 

Brachial  artery,  202 

Brain,  288;  dissection  of,  299; 
hygiene  of,  311 

Bread,  composition  of,  116; 
wheaten.  superiority  of,  120 

Breastbone,  27,  34 

Bright's  disease,  266  (foot-note) 

Bronchi,  235 

Bronchitis,  237 

Brunner,  glands  of,  148 

Buccal  cavity  (See  mouth  cavity) 

Butter,  117 

Butyriu,  117 

CABBAGE,  nutritive  value  of,  121 

Caecum,  148,  170 

Calcium  carbonate,  20,  55 

Calcium  phosphate,  20,  55,  57 

Calcaneum,  (heel  bone)  42 

Calices  of  kidney,  263,  278 

Canaliculi  of  bone,  54 

Cane  suu'ar,  118 

Canine  teeth,  136 

Capillaries,  195,  204;  absence  of 
pulse  in,  226;  circulation  in, 
224.  225;  demonstration  of  the 
action  of,  232;  pulmonary, 
199;  systemic,  198 

Capsular  ligament,  61 

Carbohydrates  (amyloids),  22, 
118;  kinds  of  in  the  body, 
22 

Carbonate  of  lime,  20,  55 

Carbon  dioxide,  as  -a  waste  pro- 
duct, 105  ;  demonstration  of 
presence  of  in  expired  «,ir, 
259;  in  the  blood,  184;  p<>r- 
centage  of  in  unwholesome  air, 
255;  quantity  of  passed  from 
the  lunsrs  in  a  day,  252;  useless 
as  a  food,  112 

Cardiac  impulse  (apex  beat),  217 

Cardiac  orifice  of  stomach,  143, 
170 


Cardiac  period,  events  occurring 
in  a,  217 

Carotid  arteries,  202 

Carpal  bones,  28,  51;  joints  be- 
tween, 65 

Carrots,  nutritive  value  of,  121 

Cartilage,  articular,  26.  48;  cells 
of,  23;  costal,  34;  function  of, 
33;  intervertebral,  30.  33 

Casein,  21,  117;  vegetable,  117 

Cells,  15,  17;  air,  of  lungs,  237: 
cartilage,  23  ;  ciliated,  of  air 
passages,  236;  forms  of,  15; 
nerve,  297;  plain  muscle,  76; 
structure  of,  15 

Cellulose,  116,  164 

Cement  of  teeth,  137 

Centres,  nerve  (see  Nerve-cen- 
tres) 

Centre  of  gravity  of  body,  85 

Centrum  of  vertebrae,  30 

Cerebellum,  289;  functions  of, 
306;  removal  of.  313 

Cerebral  hemispheres,  289;  re- 
moval of,  812 

Cerebro-spinal  liquid,  286 

Cerebro  -  spinal  nerve  system, 
284 

Cervical  enlargement  of  spinal 
cord,  287 

Cervical  vertebrae,  30 

Cheese,  nutritive  value  of,  120 

Chemical  changes  in  respired  air, 
251 

Chemical  composition  of  albu- 
mens, 21 ;  of  bile,  161 ;  of  blood- 
serum,  182;  of  body,  19;  of 
bone,  54;  of  carbohydrates.  22; 
of  fats,  21 ;  of  gastric  juice,  156; 
of  lymph,  189;  of  muscle,  77; 
of  pancreatic  secretion,  159;  of 
red  corpuscles,  183;  of  respired 
air,  252 

Chest  (see  Thorax) 

Chloral,  361 

Chordae  tendinese,  201,  214 

Choroid,  321 

Chyle,  158 

Chyme.  158 

Cilia,  236;  demonstration  of  ac 
tion  of,  249 

Circulation,  107,  207;  in  capilla- 


368 


INDEX, 


Circulation  (Continued). 

ries and  veins.  224;  portal,  208; 

pulmonary,  208;  systeftwc,  208; 

diagrfflfe  of,  209 
Circulatory  organs,  192;  relation 

of  to  excretion,  108;   diagram 

of,  194 

Circu induction,  63 
Circumvallate  papillae,  139,  334 
Clavicle  (collar  bone),  27 
Clotting  of  blood  (see  Coagula- 
tion) 
Coagulation  of  blood,  179;  cause 

of,  180;  experimentsunon,  190; 

uses  of,  181 
Coccyx,  30 
Cochlea,  331 
Coeliac  axis,  202 
Coffee,  123 
Cold,  taking,  229 
Collar-bone  (clavicle),  27 
Colloids,  157 
Colon,  149,  170 
Colorless  blood  corpuscles,  179, 

190 

Columnae  carnese,  215 
Comminuted  fracture  of  bones, 57 
Common  bile-duct  (ductus  corn- 
munis  choledochus),  150,  170 
Compact  bone, 49;  structure  of,  51 
Compound  fracture  of  bone,  58 
Concha,  330 

Condiments  as  foods,  115 
Connective  tissue,  24 
Conservation  of  energy,  law  of, 

93;  illustrations  of,  94 
Consonants,  classification  of,  341 
Constructive  power  of  the  body, 

112 

Convolutions  of  the  brain,  290 
Cooking,  123 

Co-ordination,  281;  centre  of,  306 
Corium  (cutis  vera,  dermis),  268; 

papillae  of,  270 
Corn,  nutritive  value  of,  121 
Cornea,  321 

Coronary  arteries,  199,  202,  213 
Coronary  sinus,  214 
Coronary  veins,  200,  213 
Corpus  Arantii,  214 
Corpuscles  of  blood,  176,  190 
Costal  cartilage,  34 


Costal  respiration,  246 
Cranial  nerves,  290;  sutures,  38 
Cranium,  bones  of,  37 
Cricoid  cartilage,  338 
Crystalline  lens,  325 
Crypts  of  Lioberkiihn,  148 
Cuticle  (epidermis),  266 

DEATH,  from  starvation.  98;  from 
alcohol,  347,  352,  3o3;  from 
chloral,  363;  from  opium  or 
morphia,  361 

Death-stiffening  (rigor  mortis),  74 

Defibrinaied  blood,  181  [355 

Degeneration,  fatty,  354;  .abrous, 

Deglutition  (see  Swallowing) 

Delirium  tremens,  352 

Dentine,  136 

Dermis  (see  Corium) 

Dir  jysis  (osmosis),  186 

Diaphragm  (midriff),  11,  242;  de- 
monstration of,  248 

Diarrhoea,  229 

Die?,  advantages  of  a  mixed,  125 

Digestion,  107,  128;  gastric,  157, 
171°  influence  of  saliva  in,  154; 
intestinal,'  163;  object- of,  152 

Dipsomania,  353  ' 

Disassimilation,  108 

Diseases  due  to  alcohol,  350;  to 
chloral,  362;  to  morphia  or  opi- 
um, 360;  to  tobacco,  363 

Dislocations,  65;  reduction  of,  66 

Division  of  labor,  physiological, 
17 

Dorsal  (neural)  cavity,  7,  31 ;  con- 
tents of,  9,  13 

Dorsal  vertehrae,  30 

Duct  of  glands,  101 

Duct,  common  bile,  150,  170;  cys- 
tic, 150;  hepatic,  150;  of  parotid 
-land,  169;  of  submaxillary 
gland,  169 

Dura  mater,  285 

Dyspepsia,  164 

EAR,  330 

Efferent  (motor)  nerves,  305 
Eggs,  nutritive  value  of,  120 
Egg-albumen,  21,  117 
Eighth   pair    cranial    (auditory/ 
norves,  293 


INDEX. 


869 


Elasticity  of  the  arteries,  226, 
232;  of  the  lungs,  238 

Elastic  tissue,  164 

Elbow  joint,  65,  70 

Elements  found  in.  the  bod}T,  20 
(foot-note) 

Eleventh  pair  cranial  (spinal  ac- 
cessory) nerves,  293 

Einmetropic  eye,  327 

Emulsion,  160 

Enamel,  136 

Endolymph,  331 

Endos'keleton,  23  (foot-note) 

Energy,  93,  101;  chief  forms  of 
expended  by  the  body,  101; 
conservation  of,  93,  101;  liber- 
ation of  by  oxidations  at  low 
temperature,  104;  source  of  in 
the  body,  95 

Epidermis,  266 

Epiglottis,  142,  338 

Ethmoid  bone,  37 

Eustacliian  tube,  141,  330 

Excretion  and  reception,  inter- 
mediate steps  between,  106 

Excretions,  removal  of,  108 

Excretory  organs,  106 

Exercise,  90 

Exoskeletou,  23  (foot-note) 

Expiration,  242,  244 

Extension  at  joints.  63 

Extensor  muscles,  80 

External  auditory  meatus,  330 

Extracts  of  meat,  78 

Eye,  action  of  alcohol  on,  358; 
accommodation  of,  326;  hy- 
giene of,  328 

Eyeball,  anatomy  of,  321 

Eyelashes,  318 

Eyelids,  318 

Eye-socket,  318 

FACE,  bones  of,  37 

Facial  nerve,  293 

Fasciculi  of  muscles,  73 

Fatty  acids.  117 

Fats  (hydrocarbons),  21,  117;  ab- 
sorption of,  162;  action  of  bile 
on,  161,  172;  of  gastric  juice 
on,  157;  of  pancreatic  secretion 
on,  160,  172;  as  a  reserve 


Fats  (Continued). 

food,  98,  102;  emulsifying  of, 
160^163;  kinds  of  in  body,  21 

Fauces,  141 ;  isthmus  of  the,  133, 
155;  pillars  of  the,  141 

Femoral  artery,  204 

Femur,  28 

Fibres,  16  ;  plain  muscle,  76; 
striped  muscle,  74 

Fibrillse,  74 

Fibrin,  21,  180 

Fibula  (peroueal  bone),  28,  51 

Fifth    pair    cranial    (trigeminaI)N. 
nerves,  292 

Filiform  papillae,  139,  334 

Flexion  at  joints,  63 

Flexor  muscles,  80 

Food,  amount  of  required  daily, 
124;  as  a  force  generator,  115; 
as  a  force  regulator,  115;  as 
a  machinery  former,  114;  as 
a  tissue  former,  110;  composi- 
tion of,  111;  cooking  of,  123; 
definition  of,  114;  inorganic, 
118;  is  alcohol  a  food,  121, 
343;  need  of,  95,  97;  non  oxi- 
dizable,  113;  nutritive  value 
of  different,  119;  special  im- 
portance of  albuminous,  111; 
supply  of  animal,  112 

Food-stuffs  (see  Alimentary  prin- 
ciples) 

Foot,  skeleton  of.  29;  peculiari- 
ties of  human,  45 

Fonim^n-  intervertebral.  32; 
magnum,  37;  oval,  331 

Force-generating  foods,  115 

Force-regulating  foods,  115 

Forearm,  movements  of,  64,  70 

Fore  limb  (see  Upper-limb) 

Fossa,  gleuoid,  63 

Fourth  pair  cranial  (pathetici) 
nerves,  292 

Fractures  of  bones,  57 

Free  (floating)  ribs,  34 

Frog's  web,  circulation  in,  224 

Frontal  bone,  37 

Fruits,  nutritive  value  of,  121 

Fundus  of  stomach,  170 

Fungiform  papillae,  139,  334 

Furred  tongue,  140 


370 


INDEX. 


GALL  (see  Bile) 

Gall  bladder,  150 

Games,  use  of,  92 

Ganglia,  284;  Gasserian,  292; 
spinal,  287;  sympathetic,  294 

Gases  of  the  blood,  183 

Gasseriau  ganglion.,  292 

Gastric  digestion,  157;  experi- 
ments illustrating,  171 

Gastric  glands,  144 

Gastric  juice,  144,  156;  artificial, 
171 

Gelatine,  55,  117 

Gelatiiiization,  stage  of  in  coagu- 
lation, 179 

Glands.  129;  forms  of,  131;  gas- 
tric, 144;  kinds  of,  129;  lachry- 
mal, 319;  mammary,  11;  mei- 
bomian,  318;  of  Bruuuer,  148; 
of  skin,  272;  of  small  intes- 
tine, 148;  salivary,  140,  169 

Gleuoid  fossa,  63 

Gliding  joints  (arthrodia),  65 

Glosso-pharyngeal  nerves,  293 

Glottis,  335 

Glucose  (grape  sugar),  22,  118; 
conversion  of  starch  into,  153 

Gluten,  117,  120 

Glycerine,  21,  117 

Glycocholic  acid,  161 

Glycogen,  22,  118.  151,  167 

Grape  sugar  (see  Glucose) 

Gray  nerve  fibres,  296 

Gullet  (see  (Esophagus) 

Gums,  118,  134 

HABITS,  309 

Haemal  cavity  (see  Ventral  cavity) 

hemoglobin,  178,  210,  258 

Hairs,  270 

Hair-follicle,  271 

Hand,  skeleton  of,  28 

Hard  palate,  133 

Haversian  canals,  52 

Haversian  system,  53 

Hearing,  329 

Heart,  9  action  of  alcohol  on, 
349,  357;  beat  of,  216;  cavi- 
ties of,  197;  dissection  of, 
21  wj  xperiments  upon,  230; 
position  of,  ^95;  how  nour- 
ished, 199;  muscle  of,  76;  pul- 


Heart  (Continued). 
pitatiou    of,    144;    sounds  of, 
220;    vessels  connected    with, 
198;  work  done  by  daily,  221 
Heat  of  body,  source  of,  96;  in- 
fluence of  starvation  upon,  97 
Hepatic  artery,  150 
Hepatic  duct,  150 
Hepatic  veins,  209,  212 
Hibernation,  98  (foot-note) 
High  heels,  bad  effects  of,  56 
Hilus  of  kidney,  2(53,  278 
Hind  limb  (see  Lower  limb) 
Hinge  joints  (ginglymi),63 
Hip-joint,  28,  60 
Histology,    definition,  of,    2;    of 
blood;  176;  of    bone,    51;    of 
kidneys,   265;    of    lungs,  237; 
of  lymph,  189;  of  muscle,  74; 
of  nerve  cells,  297;    of  nerve 
fibres,   296;  of  retina,  321;  of 
skin,  266 

Hollow  veins  (see  Venae  cavse) 
Human   anatomy,  definition   of, 

2,  17 
Human  physiology,  definition  of, 

1,  2,  17 

Humerus,  28,  47 
Hunger,  316 
Hydrocarbons  (see  Fats) 
Hydrochloric  acid.  20,  157 
Hygiene,   definition   of,  1,  2;  of 
blood,   184;  of  bony  skeleton, 
56;  of  brain,  311;  of  eyes,  328; 
of  muscles,  89 :  of  respiration, 
245,    254;    of    skin,    274;    of 
teeth,  137 
Hyoid  bone,  26 
Hypermetropia,  328 
Hypoglossal  nerves,  293 

ILEO-COLTC  valve,  149 

lleum,  145 

Iliac  arteries,  204 

Incisors,  1155 

Incus  (anvil  bone),  331 

Indigestible  substances,  164 

Inferior  maxillary  bone  (mandk 

ble),  37 

Inferior  maxillary  nerve,  292 
Inferior  turbimite  bone,  38,  333 
Innominate  artery,  202 


INDEX. 


371 


Innominate  bone  (os  innomina- 

tum  or  pelvic  bone),  28,  60 
Inorganic     constituents    of    the 

body,  20 

Inorganic  foods,  118 
Insertion  of  muscles,  70 
Inspiration,  242,  244 
Intercellular  substance,  16,  23 
Internal  ear  (labyrinth),  331 
Intervertebral  foramina, 32;  discs, 

30,  33 

Intestinal  digestion,  163 
Intestinal   juice   (succus    enteri- 

cus),  163 
Intestines,     digestion     in,     163; 

large,  148  (see  Large  intestine); 

small,  145  (see  Small  intestine) 
Invertebrate  animals,  character 

istics  of,  8 

Involuntary  muscles,  75 
Iris,  321 
Isthmus  of  the  fauces,  133,  155 

JEJUNUM,  145 

Joint,  ankle,  83;  elbow,  65,  70; 
hin.  28,  60;  knee,  63;  shoulder, 
42,  63 

Joints,  25;  ball  and  socket,  62; 
general  structure  of,  60;  glid- 
ing, 65;  hinge,  63;  pivot,  64; 
movements  at,  63 

KIDNEYS,  9,  261,  278:  action  of 
alcohol  on,  355,  357  ;  gross 
anatomy  of,  263;  histology  of, 
265;  secretion  of,  266, 

Knee-cap  (patella),  29 

Knee-joint,  63 

LABOR,  physiological  division  of, 

Labyrinth  (internal  ear).  331 
Lachrymal  apparatus,  319 
Lachrymal  bones,  38 
Lacteals,  147,  168.  188 
Lactose  (milk  sugar),  22,  118 
Lacunae  of  bone,  54 
Lamellae  of  bone,  53 
Large  intestine,  133, 148;  absorp- 
tion from.  168 

Larynx,  235,  337;  muscles  of,  339 
Log,  skeleton  of,  28 


Levers  in  the  body,  80,  81,  82,  83, 
84 

Lieberkiihn,  crypts  of,  148 

Liebig's  extract  of  meat,  78 

Ligaments,  24,  61;  capsular,  61; 
round,  61 ;  transverse,  of  atlas, 
32,  64 

Light,  action  of,  on  the  retina, 
323,  325 

Limbs,  comparison  of  upper  and 
lower,  38;  general  structure  of, 
10 

Liver,  149;  action  of  alcohol  on, 
357;  functions  of,  151 

Localization  of  skin-sensations, 
332 

Local  sign,  332 

Locomotion,  86 

Long  bones,  51 

Long  sight  (hypermetropia),  328 

Lower  jaw,  bone  of,  37;  move- 
ments of,  64 

Lower  limb,  comparison  of  up- 
per and,  38;  peculiarities  of,  in 
man,  45;  skeleton  of,  28 

Lumbar  enlargement  of  spinal 
cord,  287 

Lumbar  vertebrae,  30 

Lungs,  8,  106,  237;  action  of  al- 
cohol on,  357;  changes  under- 
gone by  blood  in,  257;  de- 
monstration of  the  action  of, 
248;  dissection  of,  247;  elas- 
ticity of,  238;  expansion  of, 
239 ;  quantity  of  CO2  passed  out 
from,  in  a  day,  252;  quantity 
of  O  taken  up  by,  in  a  day,  252; 
renewal  of  air  in,  240 

Luuula  of  nails,  271 

Lymph,  186;  chemistry  of,  189; 
histology  of,  189;  renewal  of, 
187 

Lymphatics  of  small  intestine, 
147 

Lymphatic  vessels  (absorbents), 
188 

MALAR  bone,  38 
Malleus  (hammer)  bone,  331 
Malpighi,  pyramids  of,  264.  278 
Mammalia,  definition  of,  11,  13 
Mammary  glands,  11 


372 


INDEX. 


Man,  as  a  vertebrate  animal,  7 
13;  place  of, among  vertebrates, 
11,  13 

Mandible  (inferior  maxillary 
bone),  37 

Margarin,  117 

Marro./,  49,  50;  red,   50 

Maxilla  (superior  maxillary 
bone),  38 

Meat  extracts,  78 

Meats,  cooking  of,  124;  nutritive 
value  of,  119 

Medulla  oblongata,  289 

Medullary  cavity  of  bone,  49,  51 

Medullary  sheath  of  nerves,  296 

Meibomian  follicles,  318 

Membranes  of  the  brain  and 
spinal  cord,  285 

Mesenteric  arteries,  202 

Mesentery,  170 

Metacarpal  bones,  28,  51 

Metatarsal  bones,  29,  51 . 

Microscopic  anatomy  (see  His- 
tology) 

Midriff  (see  Diaphragm) 

Milk,  as  a  food,  57;  nutritive 
value  of,  120;  sugar  (lactose), 
22,  118;  teeth,  135 

Mitral  valve,  201,  215 

Molar  teeth,  136 

Moral  deterioration  due  to  alco- 
hol, 361 

Morphia,  361 

Motor  (efferent)  nerves.  305 

Motores  oculi  nerves,  291 

Mouth-cavity,  133;  absorption 
from,  166 

Movements,  at  joints,  63;  of  the 
body,  how  effected,  59;  in 
sp;ice,  86 

Mucin,  164 

Mucous  coat,  small  intestine,  146 

Mucous  membrane,  of  air-pas- 
sages, 236;  of  alimentary 
canal,  128 

Mumps,  140 

Muscles,  59,  67;  chemical  com- 
position of,  77;  contraction  of, 
69.  gross  structure  of,  73;  his- 
tology of,  74;  how  controlled, 
72;  hygiene  of,  89;  of  arteries, 
228;  of  heart,  76;  of  larynx, 


Muscles  (Continued). 

339;  of  small  intestine,  148;  of 
stomach,  144;  origin  and  in- 
sertion of,  70;  papillary,  201. 
214,  219;  parts  of,  67;  rectus 
abdominis,  72;  special  physi- 
ology of,  80;  varieties  of,  71 

Muscular  fibres,  74 

Muscular  tissue,  striped,  73; 
plain,  74 

Muscular  work,  influence  of 
starvation  upon,  97;  source,  93 

Mustard,  use  of,  as  a  food,  115 

Myopia,  327 

Myosiu,  21,  77,  117, 

NAILS,  271 

Narcotics,  343 

Nares,  posterior,  38 

Nasal  bones,  38 

Nerves,  cranial,  290;  kinds  of, 
294;  spinal,  287 

Nerves,  inferior  maxillary,  292; 
ophthalmic,  292;  right  phrenic, 
212;  sciatic,  299;  superior  max- 
illary, 292;  sympathetic,  294 

Nerve- eel  Is,  297 

Nerve  centres,  282,  284;  classifi- 
cation of,  305;  functions  of, 
304 

Nerve-fibres,  afferent  and  effe- 
rent, 305;  kinds  of,  295 

Nerve-ganglia,  284 

Nerve-trunks,  382;  functions  of, 
304 

Nervous  system,  anatomy  of, 
282;  properties  of,  301,  312 

Neural  arch,  31 

Neural  cavity  (see  Dorsal  cav- 
ity) 

Nicotin;  363 

Ninth  pair  cranial  (glosso-pha- 
ryngeal)  nerves,  293 

Nitrogen-excreting  organs,  gene- 
ral arrangement  of,  261 

Non-oxidizable  foods,  113 

Non-vascular  tissues,  175 

Nucleolus,  15 

Nucleus,  15 

Nutrition,  109 

Nutritive  value  of  different 
foods,  119 


INDEX. 


,       373 


OCCIPITAL  bones,  37;  condyles, 
33 

Odontoid  (tooth-like)  process  of 
the  axis,  32,  64 

Odorous  substances,  333 

(Esophagus  (gullet),  8.  133,  142, 
169;  absorption  from,  166 

Oils    (see  Fats) 

Oil  glands  (sebaceous  -  glands), 
273 

Oleic  acid,  21 

Oleine,  21,  117 

Olfactory  lobes,  289 

Olfactory  nerves,  290 

Omentum,  13,  170 

Ophthalmic  nerves,  292 

Opium,  359 

Optic  commissures,  291 

Optic  nerves,  290,  317 

Organ,  definition  of,  4;  circula- 
tory, 107,  192,  194;  digestive, 
107,  123;  nitrogen  excreting, 
261;  of  hearing,  329;  of  sight, 
317;  of  smell,  333;  of  taste,  334, 
of  temperature  sense,  333;  of 
touch,  331;  receptive  and  ex- 
cretory, 105;  respiratory,  108, 
233 

Organic  constituents  of  the  body, 
20 

Organs  diseased  by  alcohol, 
356 

Origin  and  insertion  of  muscles, 
70 

Osinnominatum  (see  Innominate 
bone) 

Osmosis,  186 

Oval  foramen,  331 

Oxidations  in  the  body,  99 

Oxidations,  99,  100 

Oxygen,  absorption  of  from  the 
lungs,  258;  in  the  blood,  184; 
influence  of  on  the  color  of 
the  blood,  259;  quantity  of 
taken  up  by  the  lungs  in  a 
day,  252 

Oxygen  food  of  the  body,  103 

Oxyha3moglobin,  258 

PALATE,  133 
Palate  bones,  38 
Palmitic  acid,  21 


Palmitin,  21,  117 

Palpitation  of  the  heart,  144 

Pancreas,  151,  170 

Pancreatic  secretion,  159;  action 
of  on  food-stuffs,  160,  172 

Papillae  of  the  dermis,  270 

Papillae  of  the  tongue,  139 

Papillary  muscles,  201,  214;  use 
of  the,  219 

Parietal  bones,  37 

Parotid  gland,  140,  169 

Patella  (knee-cap),  29 

Pathetici  nerves,  292 

Peas,  nutritive  value  of,  121 

Pectoral  arch  or  girdle,  27;  com- 
parison of  pectoral  and  pelvic 
girdles,  38 

Pedicle  of  vetebrae,  32 

Pelvic  arch  or  girdle,  28;  com- 
parison of  pectoral  and  pelvic 
girdles,  38 

Pelvis,  28,  45 

Pelvis  of  kidney,  263 

Penniform  muscles,  71 

Pericarditis,  196 

Pericardium,  195,  212 

Perilymph,  331 

Perimysium,  73 

Periosteum,  47,  51 

Permanent  teeth,  135 

Peroneal  artery,  204 

Perspiration,  272 

Pepper,  use  of  as  a  food,  115 

Pepsin,  157 

Peptones,  157;  absorption  of.  167 

Phalanges  of  fingers,  28,  51;  of 
toes,  29,  51 

Pharynx,  133,  141;  absorption 
from,  166 

Phosphate  of  lime,  20,  55,  57 

Phrenic  nerve,  212 

Physiological  division  of  labor, 
17 

Physiology,  human,  definition 
of,  1,  2,  17 

Physiology  of  muscle,  special 
and  general,  80 

Pia  mater.  285 

Pillars  of  the  fauces,  141 

Pivot  joints,  64 

Plain  muscular  tissue,  74 

Plants,  as  food  for  animals,  112 


374 


INDEX. 


Pleura,  238 

Pleurisy,  238 

Pneumogastric  nerve,  293 

Poison,  definition  of,  116 

Polygastric  muscles,  72 

POMS  varolii,  289 

Popliteal  artery.  204 

Pork,  nutritive  value  of,  119 

Portal  circulation,  208 

Portal  vein,  150,  I7y,  208 

Posterior  nares,  38 

Potatoes,  nutritive  value  of,  121 

Premolars  (bi  cuspids),  136 

Primitive  sheath  of  nerves,  296 

Pronation,  65 

Proteid  alimentary  principles, 
117 

Proteid  substances  (see  Albumin- 
ous substances) 

Psychic  nerve  centres,  305 

Pulleys  in  the  body,  84 

Pulmonary  artery,  199,  212 

Pulmonary  circulation,  192,  208 

Pulmonary  veins,  199,  212 

Pulp  cavity  of  tooth,  136 

Pulse,  222;  disappearance  of  in 
capillaries  and  veins,  226;  hard 
and  soft,  223;  rate  of,  223 

Pupil,  321 

Pus,  179 

Pyloric  orifice  of  stomach,  143, 
170 

Pyloric  sphincter,  144,  157,  158 

Pyramids  of  Malpigh'i,  264,  278 

Racemose  (acinous)  glands,  129, 
131 

Radial  artery,  202,  222 

Radius,  28,  51 

Receptive  organs  of  the  body, 
105 

Reception  and  excretion,  inter- 
mediate steps  between,  106 

Rectum,  149.  170 

Rectus  abdominis  muscle,  72 

Red  blood -corpuscles,  composi- 
tion of,  183;  function  of,  178, 
259;  of  man,  177,  190;  of  other 
animals,  177 

Red  marrow,  50 

Reduced  haemoglobin,  210 

Reducing  dislocations,  66 


Reflex  centres,  308;  experiments 
showing  action  of,  313;  use  of, 
309 

Refracting  media  of  the  eye,  325 

Renal  arteries,  202,  261 

Renal  secretion  (urine),  266 

Renal  veins,  261 

Respiration,  108; abdominal,  246; 
chemistry  of,  250;  costal,  246; 
experiments  in,  248,  259;  hy-> 
giene  of,  245,  254;  object  of, 
233 

Respiratory  organs,  108;  anat- 
omy of,  233 

Respiratory  sounds  or  murmurs, 
245 

Retina,  317;  histology  of,  321 

Ribs,  26,  34;  action  of  in  respira- 
tion, 244 

Rice,  nutritive  value  of,  121 

Right  phrenic  nerve,  212 

Rotation  at  joints.  63 

Round  ligament,  61 

Running,  89 

SACRUM,  30,  34 

Saliva,  152,  chemical  action  of, 
153,  171;  influence  of  in  diges- 
tion, 15^;  uses  of,  152 

Salivary  glands,  140,  169 

Salt,  as  a  constituent  of  the  body, 
20,  importance  of  as  food,  118 

Sarcolemma.  74 

Scapula  (shouldor-blade),  27,  51 

Sciatic  nerve,  299 

Sclerotic,  321 

Sebaceous  glands  (oil  glands),  273 

Sebaceous  secretion,  274 

Secretion,  of  gastric  glands,  144, 
156;  of  glands  of  small  intes- 
tine, 163;  of  kidneys,  266;  of 
lachrymal  gland,  319;  of  liver, 
150,  161  (see  bile);  of  meibomi- 
an  follicles,  318;  of  pancreas, 
159  (see  Pancreatic  secretion); 
of  salivary  glands,  152  (see 
Saliva);  of  sebaceous  glands, 
274;  of  sweat  glands,  272 

Semicircular  canals,  331 

Semilunar  valves,  201,  218;  dem- 
onstration of  action  of,  231 

Semivowels,  341 


INDEX. 


375 


Sensations,  314;  common,  315; 
localization  of  skin,  332 

Senses,  special,  316 

Sensory  (afferent)  nerves,  305 

Septum  of  heart,  197.  213 

Serum  (see  Blood  serum) 

Serum  albumen,  21,  113;  coagu- 
lation of,  183,  191 

Seventh  pair  cranial  (facial) 
nerves,  293 

Shaft  of  bones,  48 

Short  bones,  51 

Short  sight  (myopia),  327 

Shoulder  gmlle(see  Pectoral  arch) 

Shoulder  joint.  42,  63 

Shower  baths,  277 

Sight,  sensation  of,  317;  organ  of, 
317 

Sigmoid  flexure,  149 

Simple  fracture  of  bones,  57 

Sinuses  of  Valsalva,  215 

Sixth  pair  cranial  (abducentes) 
nerves,  292 

Skeleton,  append icular,  27;  axi- 
al, 26;  composition  of,  23;  of 
cranium,  37;  of  face,  37;  of 
lower  limb,  28;  of  upper  limb, 
28;  peculiarities  of  human,  43 

Skin,  266;  action  of  alcohol  on, 
356:  as  a  sense-organ,  274; 
glands  of,  272;  histology  of, 
266;  hygiene  of,  274;  Vensa. 
tions,  localization  of,  332 

Skull,  26,  35;  peculiarities  in  the 
position  of,  43 

Small  intestine,  133.  145,  170; 
absorpfion  from,  167;  glands 
of,  148;  lymphatics  of,  147; 
mucous  coat  of,  146;  muscular 
coat  of,  148;  villi  of,  146 

Smell,  333 

Sounds  of  the  heart,  220 

Sounds,  respiratory,  245 

Sound  waves,  action  of  on  the 
ear,  331 

Special  physiology  of  muscles,  80 

Speech,  336 

Sphenoid  bone,  37 

Spinal  accessory  nerves,  293 

Spinal  cord,  9,  286;  dissection  of, 
299 

Spinal  ganglia,  287 


Spinal  nerves,  287 

Spine  (see  Vertebral  column) 

Spinous  process  of  vertebrae 
(neural  spine),  31 

Spleen,  170 

Spongy  (cancellated)  bone,  49 

Sprains,  66 

Standing,  84 

Stapes  (stirrup  bone),  331 

Starch,  118;  action  of  bile  on, 
161;  of  gastric  juice  on,  157;  of 
pancreatic  secretion  on,  159, 
172;  of  saliva  on,  153,  171;  sol- 
uble. 124 

Starvation,  death  from,  98;  in- 
fluence of  on  muscular  work 
and  animal  heat,  97 

Stearic  acid,  21 

Stearin,  21,  117 

Sternum  (breast  bone).  27,  34 

Stimulants.  115,  122,  343 

Stomach.  8  143,  170;  absorption 
from,  167;  action  of  alcohol  on, 
350,  356;  digestion  in,  157, 
171;  glands  of,  144;  muscular 
coat  of,  144 

Striped  muscular  tissue,  73,  74 

Sub-clavian  artery,  202 

Sub  lingual  gland,  141,  169 

Sub-maxillary  gland,  140,  169 

Succus  entericus  (intestinal 
juice).  163 

Sudoriparous  glands  (sweat- 
glands),  131,  272 

Suffocation,  104,  253 

Sugar,  cane,  118;  grape  (see 
Grape-susrar) 

Sugar  of  milk  (lactose),  22.  118 

Superior  maxillary  bone,  38 

Superior  rmixillary  nerve,  292 

Supination,  64 

Swallowing  (deglutition),  154;  as 
a  reflex  action,  309 

Sweat.  272 

Sweat  (sudoriparous)  glands,  131, 
272 

Sweetbread  (see  Pancreas) 

Sympathetic  nerve  centres,  9,  12 
'284;  ganffliaof,  293 

Synovial  fluid,  61 

Sy  no  vial  membrane,  61 

Syntonin,  77,  117 


376 


INDEX. 


Systemic  circulation,  192,  208 
Systole  of  heart-beat,  216 

TABULAR  bones,  51 

Tarsal  bones,  29,  51;  joints  be- 
tween, 65 

Tarsus,  benefits  of  peculiar 
structure  of,  45 

Taste.  334 

Taurocbolic  acid,  161 

Tea,  123 

Tears,  319 

Teeth,  characteristics  of  indi- 
vidual, 135;  general  structure 
of,  134;  hygiene  of,  137;  kinds 
of,  134 

Temperature  changes  in  respired 
air,  251,  259 

Temperature  of  the  body,  96; 
regulation  of,  97;  regulation  by 
means  of  sweat  glands,  274 
(foot-note) 

Temperature  sense.  333 

Temporal  artery,  222 

Temporal  bone.  37 

Tendons,  24.  67.  69 

Tenth  pair  cranial  (pneumpgas- 
tric)  nerves,  293 

Thein,  115 

Thigh  bone  (femur),  28 

Third  pair  cranial  (motores 
oculi)  nerves,  291 

Thirst.  316 

Thoracic  aorta.  202 

Thorax,  contents  of,  11;  dorso- 
ventral  enlargement  of,  244; 
structure  of,  242;  vertical  en- 
largement of,  242 

Thyroid  cartilage,  338 

Tibia.  28,  51 

Tibial  artery,  204 

Tight  lacing,  evil  effects  of,  247 

Tissues,  classification  of,  4  (foot- 
note); connective,  24;  nerve, 
294;  non-vascular,  175;  plain 
muscular,  74;  striped  muscular, 
74;  subcutaneous  areolar,  268: 
ultimate  structure  of,  15 

Tobacco,  363 

Tongue,  139;  furred,  140 

Tonsils,  141 

Touch,  331 


Trachea  (windpipe),  8,  235;  dig 

section   of,  247;  structure   of, 

236 
Transverse  ligament  of  the  atlas, 

32,  64 

Triceps  muscle,  72 
Triceps  muscles,  definition  of,  71 
Trichina,  120    ' 
Tricuspid  valve,  201,  214 
Trigeminal  nerves,  292 
Trypsin,  160 
Tubular  glands,  129,  131 
Turbinate  bones,  38,  333 
Turnips,  nutritive  valve  of,  121 
Twelfth   pair  cranial  (hypoglos- 

sal)  nerves,  293 
Tympanic  membrane,  330 
Tympanum,  330 

ULNA,  28,  51 

Ulnar  artery,  202 

Unstriped  muscle  cells,  76 

Upper  jaw  bone,  38 

Upper  limb,  comparison  of  upper 

and  lower  limbs,  38;  skeleton 

of,  28 
Urea,  105,  111,  266;  useless  as 

food,  112 
Ureters,  263,  278 
Urethra,  263 

Urinary  bladder,  263.  278 
Urine.  "266 

Uriniferous  tubules,  265 
Uvula,  134 

VAGI,  293 

Valsalva,  sinuses  of,  215 

Valves,  auriculo- ventricular,  201, 
214,  217,  232;  ileo-colic,  149; 
of  the  heart,  demonstration  of 
their  action,  231;  of  the  veins, 
206;  semilunar,  201,  215,  218, 
231 

Valvulse  conniventes,  146 

Vascular  system,  function  of  the 
different  parts  of,  193 

Veins,  194,  205;  absence  of  pulse 
in,  226;  circulation  in,  224; 
valves  of  the,  206 

Veins,  coronary,  199,  213;  he- 
patic, 209,  212;  hollow  (venae 
cavse),  199,  212;  portal,  150, 


INDEX. 


377 


Veins  (Continued). 
170,  208;  pulmonary,  199,  212; 
renal,  261 

Vegetable  casein,  117 

Venae  cavae  (hollow  veins),  199, 
212 

Venous  blood,  178,  211 

Ventilation,  253;  methods  of,  256 

Ventral  (haemal)  cavity,  6;  con- 
tents of,  8,  13 

Ventricles,  197 

Ventricular  contraction,  218 

Vermiform  appendix,  148 

Vertebrae,  30,  51;  structure  of,  30 

Vertebral  column,  (spine,  back- 
bone), 7,  26,  30.  34,  curvatures 
of,  33;  mechanism  of,  33;  pecu- 
liarities of  human,  44 

"Vertebrate  animals,  characteris- 
tics of,  7;  classification  of,  11 
(foot-note) 

Vestibule  of  ear,  331 

Villi  of  small  intestine,  146,  170 

Visual  apparatus,  317 

Visual  centre,  317 

Visual  purple,  323 

Vitreous  humor,  325 

Vocal  cords,  338   , 


Voice,  335;  range  of  human,  340 
Voluntary  muscles,  75  (see  also 

foot-note) 
Vomer,  37 
Vowels,  340 

WALKING,  87 

Warm  baths,  277 

Wastes  of  the  body,  105;  removal 
of,  175 

Water,  as  a  constituent  of  the 
body,  20;  as  a  food,  113,  118; 
as  a  force  regulator,  115;  as  a 
waste  product,  105;  quantity 
of  lost  through  the  kidnevs, 
266;  through  the  lungs,  251; 
through  the  skin,  273 

Wheat,  nutritive  valve  of,  120 

Whipped  (defibrinated)  blood, 
181 

White  blood  corpuscles,  179,  190 

White  nerve  fibres,  295 

Windpipe  (see  Trachea) 

Wisdom  teeth,  135 

Work,  daily,  of  heart,  221;  in- 
fluence of  starvation  upon 
muscular,  97;  power  of  the 
body  to  do,  93 


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